Colloquium

מארגן/מארגנים: 
מארגן/מארגנים: 
Usual Time: 
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Previous Lectures

Prof. Oded Millo, Racah Institute of Physics, The Hebrew University of Jerusalem
26/06/2017 - 10:30

In the vast majority of superconductors, the Cooper pairs are formed from electrons with an antiparallel spin alignment and are in the spin-singlet state. In contrast, there are very few materials that show evidence for the exotic state of triplet superconductivity, in which the Cooper pairs comprise electrons with parallel spins. Such a state was predicted to emerge, under some conditions, at superconductor-ferromagnet (S-F) interfaces, and may be important for superconducting-spintronic devices. First experimental evidence for triplet superconductivity was provided by observations of long-range (much larger than the coherence length in F) spin-polarized supercurrents in S-F-S devices. To address this problem from a different angle, we employed scanning tunneling spectroscopy (STS) on various S-F bilayer systems, and our tunneling spectra reveal long-range penetration of superconducting correlations into the ferromagnet, consistent with spin-aligned triplet-pairing with a p-wave order-parameter symmetry. I will also discuss two other systems that showed clear signatures of p-wave triplet-superconductivity in the tunneling spectra. The first consists of a-helix chiral molecules deposited on Nb (a conventional superconductor), and the second comprises single layer graphene deposited on the electron-doped cuprate superconductor Pr1.85Ce­CuO4.  

 

Prof. Uri Banin, Institute of Chemistry and the Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem
19/06/2017 - 10:30

Studying the transition of properties of nanostructures as they develop from the zero-dimensional to the one-dimensional regime is significant for unravelling the modifications that occur in the electronic structure of the particle as its length to width aspect ratio is increased. Such understanding can lead to better design and control of the particle properties, with relevance for a wide range of technological applications and in particular for flat panel displays, where semiconductor nanocrystals are presently used to achieve greatly improved color quality with energy saving characteristics. The high degree of control of shape and morphology of nanoparticles in colloidal synthesis, which allows forming structures of similar composition but of different dimensionalities and shapes, open the way for probing such dimensionality effects. We will present several effects involving the 0D to 1D transition in semiconductor nano heterostructures of different morphologies including “sphere in a sphere”, “sphere in a rod” and “rod in a rod”. Further effects of a graded shell composition, a novel rod-couples architecture and dumbbells morphology will also be described. 

Dr. Amir Bashan, Physics Department, Bar-Ilan University
12/06/2017 - 10:30

Many real-world complex systems are composed of interacting entities, where their measured activity is a result of underlying complex, usually nonlinear, dynamics. Examples of such network-based dynamical models include: biochemical, ecological and regulatory dynamics. Understanding the underlying dynamics is a key in order to control those systems. Indeed, theory of nonlinear dynamics in mathematics and statistical physics provide deep and detailed understanding of such systems. Yet, the main challenge is that most of the available data comes from snapshots originated in different individuals, and thus is considered as insufficient to extract the actual underlying dynamics, which remain unknown. I will present a novel approach to address this gap between the theory of nonlinear dynamics and the available data from dynamical systems. The approach will be demonstrated on two systems: (i) the human microbiome, the ecological community of microbes living in and on our body, and (ii) gene regulatory networks in human cells. 

Gregory Falkovich, Department of Physics of Complex Systems, Weizmann Institute of Science
05/06/2017 - 10:30

Quantum-critical strongly correlated systems feature universal collision-dominated collective transport. Viscous electronics is an emerging field dealing with systems in which strongly interacting electrons flow like a fluid. We identified vorticity as a macroscopic signature of electron viscosity and linked it with a striking macroscopic DC transport behavior: viscous friction can drive electric current against an applied field, resulting in a negative resistance, recently measured experimentally in graphene. I shall also describe current vortices, expulsion of electric field, conductance exceeding the fundamental quantum-ballistic limit and other wonders of viscous electronics. Strongly interacting electron-hole plasma in high-mobility graphene affords a unique link between quantum-critical electron transport and the wealth of fluid mechanics phenomena.

Oren Tal, Department of Chemical Physics, Weizmann Institute of Science
29/05/2017 - 10:30

The inherent electronic mismatch between molecules and metals is a general limitation for efficient electron transport in molecule-based electronics, including organic light emitting diodes, nanoscale organic spin-valves, and single-molecule transistors.

In this talk, I will review our recent progress in revealing an upper limit for conductance across metal-single molecule interfaces [1], as well as extreme spin filtering and unusual magneto-transport effects in metal-oxide junctions [2] and half-metallic molecular junctions. These findings can be used to derive general principles for efficient charge and spin transport manipulations at the atomic scale [1-4].

References:

[1] T. Yelin, R. Korytár, N. Sukenik, R. Vardimon, B. Kumar, C. Nuckolls, F. Evers & O. Tal, Nature Materials, 15, 444 (2016).      

[2] R. Vardimon, M. Klionsky & O Tal, Nano Letters, 15, 3894 (2015).

[3] D. Rakhmilevitch, R. Korytár, A. Bagrets, F. Evers & O. Tal, Physical Review Letters 113, 236603 (2014).

[4] D. Rakhmilevitch, S. Sarkar, O. Bitton, L. Kronik & O. Tal, Nano Letters 16, 1741 (2016).

 

Shlomo Havlin, Physics Department, Bar-Ilan University
22/05/2017 - 10:30

A framework for studying the vulnerability and the recovery of networks of interdependent networks will be presented.

 In interdependent networks, when nodes in one network fail, they cause dependent nodes in other networks to also fail. 

This may happen recursively and can lead to a cascade of failures and to a sudden fragmentation of the system.
I will present analytical solutions for the critical thresholds and the giant component of a network of n interdependent networks.   I will present examples of applying our model to real  interacting networks.

I will also show, that the general theory has many novel features that are not present in the classical network theory. 

When recovery of components is enabled, global spontaneous recovery of the networks and hysteresis phenomena occur

 and the theory suggests an optimal repairing strategy for a system of systems.
I will also show that interdependent networks embedded in space are
significantly more vulnerable compared to non embedded networks. In particular, small localized attacks of zero fraction 

may lead to cascading failures and catastrophic consequences.

Thus, analyzing real data and realistic models of network of networks is highly required to understand the system vulnerability.
 

References:
[1] J. Gao, S. Buldyrev, H. E. Stanley, S. Havlin, Nature Physics, 8, 40 (2012).
[2] A. Bashan et al, Nature Physics, 9, 667 (2013)
[3] A Majdandzic et al, Nature Physics 10 (1), 34 (2014); Nature Comm. 7, 10850 (2016)

[4] Daqing Li, B. Fu, Y. Wang, G. Lu, Y. Berezin, H. E. Stanley, S. Havlin, PNAS 112, 669 (2015)

[5]  J. Zhao, Daqing Li, H. Sanhedrai, R. Cohen, S. Havlin, Nature Comm. 7, 10094 (2016)  

Dimitri Roditchev - INSP, CNRS & Sorbonne University
15/05/2017 - 10:30

 

In 1964 V. L. Ginzburg predicted that new superconducting phases could appear in ultrathin films deposited on insulating surfaces. In 2010 superconductivity below 2K was discovered in some crystalline atomic monolayers of Pb grown on atomically clean Si(111) [1, 2]. Though, the amorphous Pb monolayer was found non-superconducting, but rather a correlated metal. Interestingly, Pb-monolayers can be on-demand made amorphous or crystalline, with or without presence of bulky superconducting Pb-nano-islands. This makes the Pb/Si(111) system useful to probe superconducting correlations in the vicinity of S-N or S-S’ interfaces by STM [3,4].

When two superconducting Pb-islands are linked together by a few nanometer wide non-superconducting amorphous atomic layer of Pb, superconducting correlations may propagate between the two islands, allowing a dissipation-less Josephson current to flow through the link. In the presence of a magnetic field, the Josephson vortices are expected to appear in such S-N-S Josephson junction. Josephson vortices are conceptual blocks of advanced quantum devices such as coherent terahertz generators or qubits for quantum computing, in which on-demand generation and control is crucial.

In our lecture we describe a series of recent experiments which mapped superconducting correlations in the vicinity of S-N junctions [3,4] as well as inside SNS proximity Josephson junctions using scanning tunneling microscopy [5]. By following the Josephson vortex formation and evolution we demonstrate that they originate from quantum interference of Andreev quasiparticles, and that the phase portraits of the two superconducting quantum condensates at edges of the junction decide their generation, shape, spatial extent and arrangement [5].

 

[1] T. Zhang, et al. Nature Phys. 6, 104–108 (2010).

[2] Ch. Brun, et al. Nature Phys. 10, 444 (2014).

[3] L. Serrier-Garcia, et al. Phys. Rev. Lett. 110, 157003 (2013).

[4]V.Cherkez, et al. Phys. Rev. X 4, 011033 (2014).

[5] Roditchev D., et al. Nature Phys. 11, 332 (2015).

Jay Fineberg, The Racah Institute of Physics, The Hebrew University, Jerusalem
08/05/2017 - 10:30

Friction is generally described by a single degree of freedom, a ‘friction coefficient’. We experimentally study the space-time dynamics of the onset of dry and lubricated frictional motion when two contacting bodies start to slide. We first show that the transition from static to dynamic sliding is governed by rupture fronts (closely analogous to earthquakes) that break the contacts along the interface separating the two bodies. Moreover, the structure of these "laboratory earthquakes" is quantitatively described by singular solutions originally derived to describe the motion of rapid cracks under applied shear. We demonstrate that this framework quantitatively describes both earthquake motion and arrest. A further surprise is that lubricated interfaces, although “slippery”,  actually becomes tougher; lubricants significantly increase dissipated energy during rupture. The results establish a new (and fruitful) paradigm for describing friction.

Erez Braun, Physics, Technion
24/04/2017 - 10:30

Morphogenesis, the emergence of well-defined patterns of functional tissues during development, is carried out by the collective dynamics of multiple physical and biochemical processes at different levels of organization, from local molecular events to large-scale chemical, electrical and mechanical stress fields. Morphogenesis emerges by the interaction of these various processes, which must evolve simultaneously as coupled fields. We take advantage of a unique multicellular organism, Hydra, famous for its extraordinary regeneration capabilities, to advance our biophysical understanding of morphogenesis. I will discuss our recent experiments on Hydra regeneration, shedding light on the role of the actomyosin cytoskeleton and the forces it generates during morphogenesis. We apply mechanical constraints by studying regeneration from tissue segments anchored on wires, showing that the wires induce order in morphogenesis. Finally, we utilize external force fields, hydrodynamic flows, electric fields and magnetic forces on beads attached to the regenerating tissue, to induce spatio-temporal modes during the regeneration process. Perturbing the regeneration process and imposing external constraints enable us to expose alternative developmental trajectories.

Ron Naaman, Department of Chemical Physics, Weizmann Institute
03/04/2017 - 10:30

Spin based properties, applications, and devices are commonly related to magnetic effects and to magnetic materials. However, we found that chiral organic molecules act as spin filters for photoelectrons transmission [1]  in electron transfer [2] and in electron transport [3]  .

The new effect, termed Chiral Induced Spin Selectivity (CISS) [4,5]  has interesting implications for the production of new types of spintronics devices [6]  and on electron transfer in biological systems.  The effect was found in bio-molecules and in bio-systems [7]. The basic effect will be explained and various applications and implications will be discussed.

 

  1. Göhler, B.; Hamelbeck, V.; Markus, T.Z.; Kettner, M.; Hanne, G.F.; Vager, Z.; Naaman, R.; Zacharias,  H. Science 2011, 331, 894.
  2. Mishra, D.; Markus, T.Z.; Naaman, R.; Kettner, M.; Göhler, B.; Zacharias, H.; Friedman, N.; Sheves, M.; Fontanesi, C. PNAS,   2013, 110, 14872.
  3.  Xie, Z.; Markus, T. Z.; Cohen, S. R.; Vager, Z.; Gutierrez, R.; Naaman, R. Nano Letters, 2011, 11, 4652.
  4. Naaman, R.; Waldeck, D.H. J. Phys. Chem. Lett. (feature) 2012, 3, 2178.
  5. R. Naaman, D. H. Waldeck, Spintronics and Chirality: Spin Selectivity in Electron Transport Through Chiral Molecules, Ann. Rev. Phys. Chem. 2015, 66, 263–81.
  6. Ben Dor, O.; Yochelis, S.; Mathew, S. P.; Naaman, R.; Paltiel, Y. Nature Communication, 2013, 4, 2256.
  7.  I. Carmeli, K. S. Kumar, O. Hieflero, C. Carmeli, R. Naaman,  Angew. Chemie  2014, 53, 8953 –8958.
Nir Barnea, The Racah Institute of Physics, The Hebrew University, Jerusalem
27/03/2017 - 10:30

Few years ago it was suggested by S. Tan that the properties of cold and dilute quantum gases depend on a new characteristic quantity, the ``contact''. The ``contact'' describes the probability of two particles coming close to each other, i.e. it is a measure of the number of close particle pairs in the system. Utilizing this concept, a series of theorems, already verified experimentally, predicts the macroscopic properties of the system. In my talk I will present Tan’s  ``contact'' and its generalization to nuclear systems, introducing the various nuclear contacts, and their applications.
 

Re'em Sari, The Racah Institute of Physics, The Hebrew University, Jerusalem
20/03/2017 - 10:30

Mass transfer between members of a binary is a common and well studies situation. As members of a binary become closer to each other, mass may leak from one object due to the strong tidal forces from the other. Usually, the leaking mass flows towards the companion, but we show that for main sequence stars that orbit the supermassive black hole in the galactic center and emit gravitational waves mass may also leak away from it. We show that the mass transfer affects the evolution of the gravitational wave emission in a way that reflects internal properties of the star. This may be relevant to observations of the planned LISA mission. On another front, tides may lead to orbital decay of planets which are close enough to their stars. Mass transfer will occur and we discuss its observational consequences in view of data from the Kepler mission.

יעקב קטן, המחלקה למחלות צמחים ומיקרוביולוגיה, האוניברסיטה העברית, הפקולטה לחקלאות, מזון וסביבה, רחובות
30/01/2017 - 10:30

גורמי מחלות (פתוגנים), מזיקים ועשבים גורמים נזקים רבים לגידולים חקלאיים והם פוגעים ביכולתנו לספק מזון בעולם שאוכלוסייתו גדולה ואשר בו יותר מ-800 מליון רעבים. הדברת גורמי הפגע מאפשרת העלאת היבולים. השימוש בחומרי הדברה (pesticides) הוא דרך מאוד יעילה להדברת הפגעים הללו אך השימוש בהם עלול לפגוע בסביבה ובבריאות. נעשים מאמצים לפתח  חלופות לחומרי הדברה שהן ידידותיות לסביבה אך גם יעילות בהדברה. פיתוח זני צמחים עמידים גנטית למחלות, הדברה ביולוגיות של פגעים ושיטות אחרות הנן חלופות שנחקרות וחלקן בשימוש נרחב.

בארץ פותחה שיטת החיטוי הסולרי (Soil solarization) של חימום הקרקע באמצעות יריעות פוליאתילן שקופות להדברה פתוגנים ועשבים ע"י קטילה תרמלית של הפתוגנים כחלופה לחיטוי כימי של הקרקע אשר נעשה בדרך כלל באמצעות חומרים רעילים. נערכו מחקרים רבים בארץ ובעולם (ביותר מ-70 מדינות) על היבטים מיקרוביאליים, פיסיקליים, כימיים, אגרוטכניים, טכנולוגיים, כלכליים ועוד של החיטוי הסולרי במטרה לשפר את יעילותו ולהרחיב את השימוש בו למטרות נוספות, מעבר לחיטוי קרקע.

שימו לב: ההרצאה תנתן בעברית. המרצה - חתן פרס ישראל בחקר החקלאות ומדעי הסביבה משנת תשע"ד.

Frédéric Chevy, École Normale Supéuriere, Paris, France
23/01/2017 - 10:30

In his famous lectures, R. P. Feynman highlights the deep unity of physics and the analogies existing between sometimes vastly different physical systems. In the same spirit I will demonstrate how the tools and concepts inherited from classical hydrodynamics can be used to explain the quantum world. As an example, I will show that the same phenomena govern the physics of water-walking insects and that of laser-cooled superfluid vapours.

Nirit Dudovich, Department of Physics of Complex Systems, Weizmann Institute of Science
16/01/2017 - 10:30

Attosecond science is a young field of research that has rapidly evolved over the past decade. Performing time-resolved measurements with attosecond precision is a significant challenge. The rapid progress in this field opened a door into a new area of research that allows one to observe multi-electron dynamics. Currently, two main approaches have been successfully demonstrated. The first approach, Attosecond Pump-Probe Spectroscopy, applies an attosecond pulse to initiate or probe a fast-evolving process. An alternative approach, Attosecond Self-Imaging, applies the attosecond production process, to perform the measurement.

Although attosecond spectroscopy holds great promise for both measurement and control of matter, the understanding and implementation of most processes pose significant challenges. The extreme nonlinear nature of the interaction offers numerous channels, strongly coupled by the strong laser field, in which electronic dynamics can evolve.

In the talk I will review some of the main challenges and goals in the field of attosecond science. I will describe advanced schemes in attosecond spectroscopy where the interaction is probed via several synchronized fields. Such integration probes the multidimensional nature of the interaction, thus revealing its complexity. I will then focus on a new direction that integrates the two main branches in attosecond spectroscopy – the attosecond pump-probe scheme with the self-imaging approach.  This scheme increases the dimensionality in both the measurement and control of attosecond scale processes, allowing the observation of a wide range of multielectron phenomena.

Prof. Nathalie Q. Balaban
09/01/2017 - 10:30

Noise analysis in biological systems has greatly increased our understanding of the underlyingcellular processes. Noise in the cell division process is often assumed to be responsible for variability in cell cycle duration, and to underlie heterogeneous responses of bacteria to antibiotics, as well as of cancer cells to drugs.

We show that variability of growth in bacteria can evolve under fluctuating environment.  

More generally, we ask whether we can differentiate between stochastic and deterministic control of cell division variability. Using long-term time lapse microscopy to follow thousands of divisions and tools from non linear dynamics analysis, we show that the variability in cell-cycle duration in mammalian cells, which at first glance seems dominated by noise, is in fact controlled by a deterministic factor.

 

Prof. Ady Stern
02/01/2017 - 10:30

In this talk I will review the concept of topological superconductivity, of the associated Majorana fermions, and of their recent realization using nanowires in proximity to conventional superconductors. I will then analyze the way that two dimensional Josephson junctions may be employed to create one dimensional topological superconductors and describe the unique properties of the resulting system. 

Prof. Aharon Kapitulnik
19/12/2016 - 10:30

The standard paradigm for transport in metals relies on the existence of quasiparticles. Transport coefficients such as electrical and thermal conductivities can then be calculated using e.g. Boltzmann equations. However, such an approach fails in the so-called `bad metal' regime, when the quasiparticle mean free paths become comparable to the wavelengths of the electron and/or highest frequency phonon. Transport in non-quasiparticle regimes requires a new framework and has become a subject of intense theoretical and experimental efforts in recent years.  In particular, the diffusivity was singled out as a key observable for incoherent non-quasiparticle transport, possibly subject to fundamental quantum mechanical bounds. Following a review of previous experimental results on bad metallic behavior, we will introduce new results on transport in strongly correlated electron systems with strong electron-phonon interaction. These results suggest that when neither well-defined electron nor phonon quasiparticles are present, thermal transport exhibits a collective behavior of a `soup' of strongly coupled electrons and phonons which diffuses at a unique velocity, exhibiting a saturated scattering time of ~ħ/kT.

 

Tsvi Piran, Racah Institute for Phyiscs, The Hebrew University, Jerusalem
12/12/2016 - 10:30

Gravitational waves were predicted by Albert Einstein as an outcome of the general theory of relativity in 1916. Advanced LIGO was barely switched on when the frist gravitational radiation signal ever, GW 150914, was detected. It turned out that it signaled a merger between two ~30 solar masses black holes some 1.5 billion light years away. Later on a second signal, GW 151226, was detected. I will review the physics of gravitational radiation, the advanced LIGO detector, these recent discoveries and their various implications.

Prof. Eli Sloutskin, Physics Departement, Bar Ilan
28/11/2016 - 10:30

Among all possible shapes of a volume V, a sphere has the smallest surface area A. Therefore, liquid droplets are spherical, minimizing their interfacial energy \gamma A for a given interfacial tension \gamma. We demonstrate that liquid oil droplets in water, stabilized by a common surfactant, adopt icosahedral and other faceted shapes, tunable by temperature, while still remaining liquid[1,2]. Although liquid droplets have been studied for centuries, no faceted droplets have ever been detected.

We attribute the observed transition from a spherical to an icosahedral shape to the interplay between \gamma and the elastic properties of the interfacial monomolecular layer, which in these systems crystallizes above the bulk melting point. The role of topological lattice defects in this quasi-two-dimensional crystalline surface monolayer will be discussed. The shape of the droplets is determined by the topological charge of these defects (i.e., the number of nearest neighbours missing at each defect), with the icosahedral droplets transforming on cooling into platelet-like rectangular, hexagonal, hexagram-like and other faceted shapes. In addition to faceting, we observe a wide range of other unexpected phenomena, such as a spontaneous splitting of liquid droplets. The common physical mechanism, responsible for all these effects will be demonstrated[1,2].

These phenomena allow deeper insights into the fundamentals of molecular elasticity to be gained, mimicking faceting transitions in complex biological systems and opening new horizons for a wide range of technologies, from self-assembly of complex colloidal shapes to new delivery strategies in bio-medicine.

[1] S. Guttman, Z. Sapir, M. Schultz, A. V. Butenko, B. M. Ocko, M. Deutsch, and E. Sloutskin,
Proc. Natl. Acad. Sci. USA 113, 493 (2016).

[2] S. Guttman, B. M. Ocko, M. Deutsch, and E. Sloutskin, Curr. Opin. Colloid Interface Sci. 22, 35 (2016).

Prof. Patrick Sebbah, Physics Department, Bar Ilan
21/11/2016 - 10:30

Predicting the spatial pattern of vibrational modes in complex systems remains a key scientific and engineering challenge with strong repercussions in various domains such as laser cavity design or musical instrument architecture. A recent theoretical breakthrough brings a new tool, called the "localization landscape", for retrieving crucial information on the spatial and frequency properties of these localized waves [1].

Here, this theory is tested experimentally for the first time by investigating wave localization for elastic waves in structured thin plates [2]. We show that regions of wave confinement can be predicted from the knowledge of the static deformation of the plate. These results reveal the predictive power of the "localization landscape" function, especially when a structural or microscopic description of the system is not accessible.

[1] M. Filoche, and S. Mayboroda, Proceedings of the National Academy of Sciences 109, 14761-14766 (2012).

[2] G. Lefebvre, A. Gondel, M. Dubois, M. Atlan, F. Feppon, A. Labbé, C. Gillot, A. Garelli, M. Ernoult, S. Mayboroda, M. Filoche, and P. Sebbah, Phys. Rev. Lett. 117, 074301 (2016).

Prof. Elisha Moses, Dept. of Physics of Complex Systems, Weizmann Institute of Science
14/11/2016 - 10:30

Cultured networks of neurons from hippocampus constitute a fascinating reductionist model for biological computation. While individual neurons retain the physiological characteristics as in the intact brain, the structure and connectivity in the network are considerably simpler to measure and analyze, and therefore to engineer and design. We show that disconnected single neurons oscillate independently of each other, and that when the network is connected they synchronize into periodic network bursts in which all neurons fire together. This behavior is attributed to Kuramoto-Strogatz like behavior for the synchronization of pulse-coupled oscillators. We investigate how initiation of this burst is brought about, and find that the recruitment of a minimal cohort of firing units plays a crucial role in the process. Activation of the whole network is well described by a theoretical model of percolation invoking the need for ‘quorum’ decision making.

Nini Pryds, Department for Energy Conversion and Storage, Technical University of Denmark
07/11/2016 - 10:30

 

The conductance confined at the interface of complex oxide heterostructures provides new opportunities to explore nanoelectronic as well as nanoionic devices. In this talk I will present our recent results on electronic conductivity at different heterostructures systems. I will discuss and show what is happening when two oxides intimately contact each other, charge redistribution or mass transfer of ions may occur. Our recent results of high mobile samples realized by, interface confined redox reactions [1], strain induced polarization [2] and modulation doping [3] at complex oxide interfaces. Based on the enhanced mobility we have recently studied the Quantum Hall Effect (QHE) which reveal the strength of enhancing the mobility [4]. This collection of samples offers unique opportunities for a wide range of rich world of mesoscopic physics.

 

[1]  Y. Z. Chen & N. Pryds et al. “A high-mobility two-dimensional electron gas at the spinel/perovskite interface of γ-Al2O3/SrTiO3”. Nature Commun. 4, 1371 (2013)

 [2] Y. Z. Chen & N. Pryds et al. “Creation of High Mobility Two-Dimensional Electron Gases via Strain Induced Polarization at an Otherwise Nonpolar Complex Oxide Interface” Nano Letters. 3774-3778 (2015) 10.1021/nl504622w

 [3] Y. Z. Chen & N. Pryds et al. “Extreme mobility enhancement of oxide 2DEGs via charge transfer induced modulation doping.” Nature Materials, 14 (8), 801-806 (2015)

 [4] F. Trier &N. Pryds et al., “Quantization of Hall Resistance at the Metallic Interface between an Oxide Insulator and SrTiO3” Physical Review Letters, 117, 096804 (2016)

Herb Fertig, Dept. of Physics, Indiana University at Bloomington
20/06/2016 - 10:30

In some two-dimensional systems, electrons have topological properties
which endow them with surprising transport properties.  While nature
provides us with a few such materials, their topology is limited by the materials
which can actually be synthesized.  In this talk I will review recent work
in which such topology is induced by time-dependent potentials, allowing
in principle a broad set of possibilities for topological bands to be
created. These "Floquet Topological Insulators" support
surprising fundamental behaviors,  including a quantized Hall effect with
no magnetic field, and in some cases transport enhancement by
disorder. In this talk I will discuss how these possibilities play out for electrons in graphene,
showing how a time-dependent electric field yields a rich set of topological phases,
and how they support phenomena which cannot be realized in a static setting.
 

Yitzhak Rabin
06/06/2016 - 10:30

We use computer simulations to study multi-component systems in which all the particles are different (APD). The particles are assumed to interact via Lennard-Jones potentials with identical size parameters, but with pair interaction parameters generated at random from some distribution. We analyze these systems at temperatures above and below the freezing transition and find that APD fluids relax into a non-random state characterized by clustering of particles according to the values of their pair interaction parameters (Neighborhood Identity Ordering - NIO). We study the NIO using the random bond lattice model and show that the transition from frozen to annealed disorder depends not only on temperature but also on system size. We use a variant of the APD model to study the competition between specific and non-specific interactions and show that contrary to intuitive expectations the latter can assist in the formation of specific complexes. The relevance of our results to biological systems is discussed.

Prof. Immanuel Bloch, Max-Plank-Institute for Quantum Optics, Garching, Germany
30/05/2016 - 10:30

More than 30 years ago, Richard Feynman outlined the visionary concept of a quantum simulator for carrying out complex physics calculations. Today, his dream has become a reality in laboratories around the world. In my talk I will focus on the remarkable opportunities offered by ultracold quantum gases trapped in optical lattices to address fundamental physics questions ranging from condensed matter physics over statistical physics to high energy physics with table-top experiment.

For example, I will show how it has now become possible to image and control quantum matter with single atom sensitivity and single site resolution, thereby allowing one to directly image individual quantum fluctuations as well as spin and charge correlations of a many-body system. Such ultrahigh resolution and sensitivity have also enabled us to detect ‘Higgs’ type excitations occurring at 24 orders of magnitude lower energy scales than in high energy physics experiments and to observe antiferromagnetic order in the Fermi Hubbard model. Finally, I will show how the unique control over ultracold quantum gases has enabled the realization of artificial magnetic fields of extreme field strengths that will allow to probe quantum matter in completely new parameter regimes.

Gilad Perez, Dept. of Particle Physics and Astrophysics, Weizmann Institute of Science
23/05/2016 - 10:30
After the discovery of the Higgs particle at the Large Hadron Collider, the Higgs mechanism is expected to account for all observed masses of the the fundamental, point like, particles. We briefly argue that, while this is true for the mediators of the weak force (the W and Z gauge bosons), we are still in the dark regarding the origin of the charged fermions masses. In particular, the nature of the masses of the building blocks of matter, the electron and up and down quarks is an open question, both theoretically and experimentally. 
It motivates us to propose a non-collider approach to probe Higgs boson couplings to these matter constituents via precision measurement of isotope shifts in atomic clock transitions. We present an experimental method which, given state-of-the-art accuracy in frequency comparison, competes with and potentially surpasses the Large Hadron Collider in bounding the Higgs-to-light-fermion couplings. Better knowledge of the latter is an important test of the Standard Model which could lead, besides the establishment of new physics above the weak scale, to an alternative understanding of the flavor puzzle (namely the fact that the fermions masses span five orders of magnitude in scale).
If time permits we will then discuss how to translate the above (potential) fantastic sensitivity to constrain the presence of heavy new degrees of freedom that are well beyond the reach of near future accelerators. 
Prof. Ido Kanter, Physics Department, Bar Ilan University
16/05/2016 - 10:30

Realizations of low firing rates in neural networks usually require globally balanced distributions among excitatory and inhibitory synapses, while feasibility of temporal coding is limited by neuronal millisecond precision. We show, experimentally and theoretically, that low firing rates as well as cortical oscillations stem from neuronal plasticity in the form of neuronal stochastic neuronal response failures emerge, as exemplified both in in-vitro and in-vivo experiments. Those failures appear in such a way that the neuron functions similar to a low pass filter, saturating its average inter-spike-interval. This intrinsic neuronal plasticity leads to cooperation on a network level, which suppresses the firing rates towards the lowest neuronal critical frequency simultaneously with the stabilization of the neuronal response timings to ms precision. In addition, this neuronal plasticity counterintuitively leads to the simultaneous emergence of macroscopic d and g oscillations in excitatory networks. A quantitative interplay between the statistical network properties and the emerging oscillations is supported by simulations of large networks that are based on single-neuron in-vitro experiments and a Langevin equation which describes the network dynamics. It is also supported by an experimental scheme where long-term stimulation and recording of a single neuron is used to mimic simultaneous activity measurements from thousands of neurons in a recurrent network.

Dorit Aharonov, Dept. of Computer Science, Hebrew University
09/05/2016 - 10:30

The new area of  quantum Hamiltonian complexity, which had emerged from quantum computation over the past decade, studies some of the most fundamental questions in quantum physics from a computational viewpoint.
This approach turns out to offer deep insights for physics (as well as computer science) which are now beginning to be revealed. I will attempt to describe some achievements from this fast growing vibrant area;
Connections to area laws, simulating condensed matter physics, stability of entanglement, precision measurements and even black holes will be mentioned, with emphasis on the many exciting open questions in this field.

Prof. Victor Malka, Ecole Polytechnique, Université Paris-Saclay, France and Weizmann Institute of Science
02/05/2016 - 10:30

Laser Plasma Accelerators (LPA) rely on the control of the electrons motion with intense laser pulses [1]. The manipulation of electrons with intense laser pulses allows a fine mapping of the longitudinal and radial components of giant electric fields that can be optimized for accelerating charged particle or for producing X rays. To illustrate the beauty of laser plasma accelerators I will show, how by changing the density profile of the gas target, one can improve the quality of the electron beam, its stability [2] and its energy gain [3], or by playing with the radial field one can reduce its divergence [4]. I’ll then show how by controlling the quiver motion of relativistic electrons intense and bright X-rays beam are produced in a compact and elegant way [5,6]. Finally I’ll give some examples of applications [7].

References :

[1] V. Malka, Phys. of Plasmas 19, 055501 (2012).

[2] E. Guillaume et al., Phys. Rev. Lett. 115, 155002 (2015).

[3] C. Thaury Scientific Report, 10.1038, srep16310, Nov. 9 (2015).

[4] C. Thaury et al., Nature Comm. 6, 6860 (2015).

[5] K. Ta Phuoc et al., Nature Photonics 6, 308-311 (2012).

[6] S. Corde et al., Review of Modern Phys. 85 (2013).

[7] I. Andriyash et al., Nature Comm. 5, 4736 (2014).

 

Alessandro Silva, SISSA, Trieste
11/04/2016 - 10:30

This Public Lecture is the opening talk of the Italy-Israel meeting on "Non-Equilibrium Physics: Theory and Experiments of Quantum Many Body Dynamics".

Yosi Avron, Faculty of Physics, Technion
04/04/2016 - 10:30
TBA

TBA

Yosi Avron, Faculty of Physics, the Technion
04/04/2016 - 10:30

The integer conductances in the quantum Hall effect are related to topological invariants known as Chern numbers. A different interpretation relates them to invariants known as Fredholm indices. I will give a tutorial and an introduction to the Fredholm Index interpretation of the integers in the Quantum Hall Effect.

Yigal Meir, Dept. of Physics, Ben-Gurion University
28/03/2016 - 10:30

Quantum point contacts (QPCs), are the basic building blocks of any mesoscopic structure, and display quantized conductance, reflecting the quantization of the number of transparent channels. An additional feature, coined the "0.7 anomaly", has been observed in almost all QPCs, and has been a subject of intensive debate in the last couple of decades. In the past we have attributed this feature to the emergence of a quasi-localized state at the QPC, which explains all the phenomenology of the effect. In this talk I will review the physics of the effect, and describe two new experiments, and relevant theories, one which measured the thermoelectric power through the QPC, and another which measured the conductance through length-tunable QPC. The experimental findings support the picture of the localized state(s). Interestingly, with increasing QPC length, it was found that both the 0.7 anomaly and the zero bias peak in the differential conductance oscillate and periodically split with channel length, supporting the idea that the number of the localized states increases with length, leading to an alternating Kondo effect.

Gereon Niedner-Schatteburg/Kaiserslautern University - Germany
21/03/2016 - 10:30

Clusters – in particular those of transition metals – may act like surfaces of limited size, this analogy being recognized long time ago [1,2]. We have studied the C-H bond activation of various organic molecules by naked transition metal clusters before [3], and it became mandatory to switch to simpler systems. By virtue of our tandem cryo ion trap instrument we study the adsorption kinetics of clusters under single collision conditions as well as the Infrared Multiple Photon Dissociation (IR-MPD) by application of optical parametric oscillator/amplifier (OPO/OPA) photon sources, one and two colour investigations of metal organic complexes by such technique being published [4].

Our ongoing studies of N2 and H2 cryo adsorption on Fe, Co, and Ni clusters and alike [5] revealed clearly discernible mono layer like adsorbate shells. Beyond such mere kinetics – though interesting in themselves – we recorded IR-MPD spectra of dinitrogen stretching vibrations within such [Mn(N2)m]+ cluster surface – adsorbate layer complexes by variation of their stoichiometry, n and of m alike, and in conjunction with electronic structure modelling (by DFT), and with synchrotron X-ray based studies of  spin and orbital contributions to the total magnetic moments of the isolated clusters [6].

This invited presentation shall elucidate the current state of cluster adsorbate studies under cryo conditions and in isolation. It aims to put into perspective the findings from adsorption kinetics, IR spectroscopy, DFT modelling and magnetic spectroscopy. It concludes with an outlook onto the road ahead.

This research originates from a long standing support by the DFG through the transregional collaborative research center SFB/TRR 88 3MET.de

 

[1] E. L. Muetterties, T. N. Rhodin, E. Band, C. F. Brucker, W. R. Pretzer, Chem. Rev., 1979, 79, 91-137. [2] G. Ertl, Angew. Chem. Int. Ed., 2008, 47, 3524 – 3535. [3] B. Pfeffer, S. Jaberg, and G. Niedner-Schatteburg, J. Chem. Phys. 2009, 131, 194305; L. Barzen, M. Tombers, C. Merkert, J. Hewer, and GNS, Int. J. Mass Spectrom. 2012, 330–332, 271–276; M. Tombers, L. Barzen, and GNS, J. Phys. Chem. A 2013, 117, 1197-1203. [4] Y. Nosenko, F. Menges, C. Riehn, GNS, Phys. Chem. Chem. Phys. 2013, 15, 8171; J. Lang, M. Gaffga, F. Menges, and GNS, Phys. Chem.Chem. Phys. 2014, 16, 17417 – 17421. [5] S. Dillinger, J. Mohrbach, J. Hewer, M. Gaffga, and GNS, Phys. Chem. Chem. Phys. 2015, 17, 10358. [6] S. Peredkov, M. Neeb, W. Eberhardt, J. Meyer, M. Tombers, H. Kampschulte, GNS, Phys. Rev. Lett. 2011,         107, 233401; J. Meyer, M. Tombers, C. van Wüllen, GNS, S. Peredkov, W. Eberhardt, M. Neeb, S. Palutke, M. Martins, and W. Wurth, J. Chem. Phys. 2015, 143, 104302.

Prof. D. Rapaport, Physics Department, BIU
14/03/2016 - 10:30

Emergent phenomena are especially fascinating because they are not obvious consequences of the design of the systems in which they appear, a characteristic equally relevant when attempting to simulate them. Several systems that exhibit surprisingly rich emergent behavior will be described, each studied by MD (molecular dynamics) simulation. (a) In the case of fluids studied at the atomistic level, not only can complex hydrodynamic phenomena in convecting and rotating fluids - the Rayleigh-Benard and Taylor-Couette instabilities - be reproduced within the limited length and time scales accessible to MD, but there is even quantitative agreement. (b) Modeling self-assembly processes associated with virus capsid growth reveals the ability to achieve complete, error-free shells, where paradoxically, high yields are due to reversible bond formation. (c) Studies of granular mixtures show behavior that, in the case of a rotating drum, reproduces known but counterintuitive axial and radial segregation, and in the case of a vertically vibrated layer, predicts a novel form of horizontal segregation. These simulations tend to be comparatively large and lengthy, and in some cases multiple runs are needed because the outcomes are unpredictable, so the use of GPU-based parallel computing is beneficial; the methodology involved will be outlined. While MD is subject to limitations, both conceptual and computational, the results offer exciting indications of what can be accomplished.

Liran Goren, Dept. of Geological and Environmental Sciences, Ben-Gurion University
07/03/2016 - 10:30

Bedrock rivers carve the surficial pattern of valleys and ridges that characterizes fluvial terrains in high mountains.  When tectonic forces act on the upper crust of the Earth and cause it to deform, the surface of the Earth, which is the upper boundary of the crust and the river valleys that are imprinted in the crust take part in the deformation. We have some understanding of how tectonically induced deformation reshapes the long profile of rivers and the map pattern of fluvial drainage networks, but can we solve the inverse problem of inferring rates and modes of deformation from the shape of drainage networks? In this talk I will review two field cases: one from the Basin and Range province in the US where rivers are used to infer temporal variations of tectonic uplift rates, and the second from Mount Lebanon where a suite of rivers is used to infer rates and modes of horizontal deformation along the Dead Sea fault system.

Ronny Bartsch, Dept. of Physics, Bar-Ilan
29/02/2016 - 10:30

We study sleep-stage transitions and dynamical aspects of sleep micro-architecture. 
We find that sleep-stage transitions exhibit a high degree of asymmetry, and that the entire class of sleep-stage transition pathways underlying the complexity of sleep dynamics throughout the night can be characterized by two independent asymmetric transition paths. These basic pathways remain stable under sleep disorders, even though the degree of asymmetry is significantly reduced. Our findings further demonstrate an intriguing temporal organization in sleep micro-architecture at short time scales that is typical for physical systems exhibiting self-organized criticality, and indicates non-equilibrium critical dynamics in brain activity during sleep.

Alexey Gorshkov, Joint Quantum Institute, NIST and University of Maryland
18/01/2016 - 10:30

We will first review schemes for taking advantage of the tremendous degree of control recently achieved in AMO (atomic, molecular, and optical) systems to realize topological phenomena. In particular, we will emphasize unique features of AMO systems such the abundance of bosonic platforms, accessibility of far-out-of-equilibrium dynamics, and natural occurrence of interactions decaying as tunable power laws. We will then focus on a few examples such as symmetry protected topological phases with ion crystals, various fractional quantum Hall states with dipoles, and parafermionic zero modes with ultracold neutral bosons.

Boris Altshuler, Columbia University, New York
11/01/2016 - 10:30

Strictly speaking the laws of the conventional Statistical Physics, in particular the Equipartition Postulate, apply only in the presence of a thermostat. For a long time this restriction did not look crucial for realistic systems. Recently there appeared two classes of quantum many-body systems with the coupling to the outside world that is (or is hoped to be) negligible: (1) cold quantum gases and (2) systems of qubits, which enjoy a continuous progress in their disentanglement from the environment. To describe such systems properly one should revisit the very foundations of the Statistical Mechanics. The first step in this direction was the development of the concept of Many-Body Localization (MBL) [1]:  the states of a many-body system can be localized in the Hilbert space resembling the celebrated Anderson Localization of single particle states in a random potential. Moreover, one-particle localization of the eigenfunctions of the Anderson tight-binding model (on-site disorder) on regular random graphs (RRG) strongly resembles a generic MBL.

 MBL implies that the state of the system decoupled from the thermostat depends on the initial conditions: the time averaging does not result in equipartition distribution, the entropy never reaches its thermodynamic value i.e. the ergodicity is violated. Variations of e.g. temperature can delocalize many body states. However, the recovery of the equipartition is not likely to follow the delocalization immediately: numerical analysis of the RRG problem suggests that the extended states are multi-fractal at any finite disorder [2]. Moreover, regular (no disorder!) Josephson junction arrays (JJA) under the conditions that are feasible to implement and control experimentally demonstrate both MBL and non-ergodic behavior [3].

1.  D. Basko, I. Aleiner, and B. Altshuler, Ann. Phys. 321, 1126 (2006).

2. A. De Luca, B.L. Altshuler, V.E. Kravtsov, & A. Scardicchio, PRL 113, 046806, (2014)

3. M. Pino, B.L. Altshuler and L.B. Ioffe, arXiv:1501.03853, PNAS to be published.

Martin Dressel, Physikalisches Institut, Universität Stuttgart, Germany
04/01/2016 - 10:30

Molecular solids provide the opportunity to create materials of desired properties and function­nalities by tailoring the constituents and tuning their interactions. The interplay of electronic, magnetic and lattice degrees of freedom allows us to tackle fundamental questions of competing interactions. A slight variation of the constituents and proper arrangement, for instance, causes localization of the conduction electrons, drives a Mott insulator superconducting or establishes magnetic order. The exemplary collaboration of chemists, materials scientists, experimental and theoretical physicists has advanced our understanding of organic con­ductors enormously in the last years, albeit the potential of molecular solids is far from being fully explored.

Organic charge-transfer salts are a well-established class of strongly-correlated electron sys­tems; many of them are subject to ordering phenomena in the spin or charge sector. Some of the two-dimensional quarter- filled BEDT-TTF salts are superconductors, while some of them remain metallic down to low temperatures; others undergo a sharp metal to insulator transition. Why do these materials behave electronically so differently although they are similar in structure? Optical spectro­scopy complemented by magnetic investi­gations reveals that these compounds are subject to charge order to a different degree. The interplay of charge order and superconductivity suggest superconductivity mediated by charge fluctuations.

Dr. Michael Stern, Department of Physics, Bar Ilan University
28/12/2015 - 10:30

Superconducting qubits are often considered as a leading potential candidate for the physical realization of a quantum computer. These qubits can be easily fabricated, manipulated and coupled together using simple linear electrical elements like capacitors, inductors and transmission lines. However, they suffer from rather poor coherence times due to their macroscopic size.

A promising research direction is to combine these qubits with spins in semiconductors and construct a hybrid quantum system. Indeed, spins may have extremely long coherence times and could therefore be a perfect system to reliably store the quantum information while superconducting qubits with their strong coupling with external fields are perfect systems to easily process fast quantum gates.

Efficient transfer of quantum information between these systems requires reaching the so-called “strong coupling regime” where the coupling between the different systems is much larger than their decoherence rates.  In this talk, I will present our progress and current experimental efforts in the quest for reaching the strong coupling regime between a superconducting circuit and a single spin [1-3]. 

1] M. Stern et al., Phys. Rev. Lett. 113, 123601 (2014).

[2] T. Douce et al., Phys. Rev. A, 92, 052335 (2015).

[3] A. Bienfait et al., Nature Nanotechnology, 282,1038 (2015).

 

Uri Alon, Dept. of Molecular Cell Biology, Weizmann Institute
21/12/2015 - 10:30

Organisms, tissues and molecules often need to perform multiple tasks. But usually no phenotype can be optimal at all tasks at once. This leads to a fundamental tradeoff. We study this using the concept of Pareto optimality from engineering and economics. Tradeoffs lead to an unexpected simplicity in the range of optimal phenotypes- they fall on low dimensional shapes in trait space such as lines, triangles and tetrahedrons. At the vertices of these polygons are phenotypes that specialize at a single task. One does not need to know the tasks in advance; tasks  can be inferred from the data. We demonstrate this using animal and fossil morphology, bacterial and stem-cell gene expression and other biological systems.

Prof. Eli Barkai, Department of Physics, Bar Ilan University
07/12/2015 - 10:30

Starting with the work of Bernamont (1937) on resistance uctuations, noisy signals of a vast number of natural processes exhibit 1/f power-spectrum. This power spectrum is non-integrable implying that the total energy in the system is infnite. As pointed out by Mandelbrot (1950's) this infrared catastrophe suggests that one should abandon the stationary mind set and hence go beyond the widely applicable Wiener-Khinchin formula for the power spectrum. Recent theoretical and experimental advances renewed the discussion on this old paradox, for example in the context of blinking quantum dots [1,2]. In this talk aging, intermittency, ergodicity breaking, and critical exponents of the sample power spectrum are discussed within a theoretical framework which hopefully provides new insight on the 1/f enigma [3].

 

[1] M. Niemann, H. Kantz, E. Barkai, Fluctuations of 1/f noise and the low frequency cutoff paradox, Phys. Rev. Lett. 110, 140603 (2013).
[2] S. Sadegh, E. Barkai, and D. Krapf, 1/f noise for intermittent quantum dots exhibits non-stationarity and critical exponents, New. J. of Physics 16 (2014)
113054.
[3] N. Leibovich and E. Barkai, Aging Wiener-Khinchin Theorem, Phys. Rev. Lett. 115, 080602 (2015).

Eva Andrei, Dept. of Physics and Astronomy, Rutgers University,
30/11/2015 - 10:30

Since its first scotch-tape extraction from graphite in 2004, Graphene – a one atom-thick crystal of carbon - has metamorphosed from the poor relative of diamond into a “wonder material”. By now it has amassed an impressive string of superlatives (lightest, thinnest, strongest material, best electrical and thermal conductor) and a host of close 2D relatives extracted from other layered materials. Due to their remarkable properties 2D materials are rapidly moving from research laboratories into industrial, medical and electronics applications. For physicists much of the continuing excitement about graphene stems from its exotic charge carriers - Dirac fermions - which resemble two dimensional massless neutrinos.  I will review the story and physics of graphene  with emphasis on its fascinating electronic properties as viewed through scanning tunneling microscopy and Landau level spectroscopy experiments performed in my group.

Prof. Eytan Domany, Dept of Physics of Complex Systems, Weizmann Institute of Science
23/11/2015 - 10:30

My move from Theoretical Physics to Biology has exposed me to quite a few significant differences between the disciplines. I try to describe some of these and to point out the aspects of this momentous move that were gratifying and those which I found frustrating. I assume some basic knowledge of Biology, but will try to explain things in a way that will be understandable to a Physics audience. While the talk may be perceived as provocative by some, I do promise that it will not be boring!

Prof. Yaron Silberberg, Department of Physics of Complex Systems, Weizmann Institute of Science
16/11/2015 - 10:30

Random quantum walk is the process describing the motion of a quantum particle that hops randomly, yet coherently, from site to site on a lattice. The coherent motion induces a big difference between quantum walks, for example the motion of an electron in a lattices, and classical random walks, that are responsible for processes such as molecular diffusion. We study quantum walks of photons in 'photonic lattices' that are made of arrays of optical waveguides that are close enough to allow photons to hop between them. Such lattices have been used for more than a decade to study some of the most basic phenomena of wave propagation in periodic and quasi-periodic structures, from Bloch Oscillations to Anderson Localization.  While most work with photonic  lattices have studied wave propagation using coherent laser light, we have shown that they could also serve as an excellent platform for the study of quantum dynamics, and in particular of quantum walks. We have extended this concept to more complex random walks of several particles, and have shown that such walks by indistinguishable particles lead to new and surprising effects on the quantum correlations of the co-propagating walkers in periodic lattices. Even more surprises are found when the quantum walkers move in a disordered lattice where the particles are also constrained via Anderson localization, and I will present recent experiments on such systems.

Barak Kol, Racah Institute of Physics, Hebrew University
09/11/2015 - 10:30

The two body problem in Einstein's gravity has both intrinsic theoretical interest, as well as importance for the ongoing observational search for gravitational waves. This talk will explain how field theory ideas and techniques were used to perturbatively solve the two-body problem in the slow velocity post-Newtonian limit. Central notions include the two-body effective action, field elimination through Feynman diagrams, a non-relativistic decomposition of Einstein's field, and finally divergences, their regularization and renormalization. This approach is known as the Effective Field Theory approach to General Relativity.

Moty Heiblum, Dept. of Condensed Matter Physics, Weizmann Institute
02/11/2015 - 10:30

Electron pairing is a rare phenomenon appearing only in a few unique physical systems; e.g., superconductors and Kondo-correlated quantum dots. Here, we report on an unexpected, but robust, electron ‘pairing’ in the integer quantum Hall effect (IQHE) regime. The pairing takes place within an interfering edge channel circulating in an electronic Fabry-Perot interferometer at a wide range of bulk filling factors, 2<νB<5. The main observations are: (a) High visibility Aharonov-Bohm conductance oscillations with magnetic flux periodicity Delta(φ)=ϕ0/2=h/2e (instead of the ubiquitous h/e), with e the electron charge and h the Planck constant; (b) An interfering quasiparticle charge e*~2e - revealed by quantum shot noise measurements; and (c) Full dephasing of the h/2e periodicity by induced dephasing of the adjacent edge channel (while keeping the interfering edge channel intact) – a clear realization of inter-channel entanglement. While this pairing phenomenon clearly results from inter-channel interaction, the exact mechanism that leads to e-e attraction within a single edge channel is not clear.

Prof. Yuval Garini, Physics Department & Institute of Nanotechnology, Bar Ilan University
26/10/2015 - 10:30

The DNA in a human cell is ~3 meters long. It is dynamic and although there are no definite structures that maintain the order in the nucleus, the genome is well organized. What are the mechanisms that organizes the DNA in the nucleus?

Dynamic methods in live cells are ideal for studying the genome organization, as it is mainly made of soft-matter that have no definite structure.

We used single particle tracking (SPT) and continuous photobleacing (CP) that are adequate for live-cell imaging and the data is analyzed according to diffusion analysis methods. In normal cells, all the sites in the genome exhibit anomalous diffusion (viscoelastic) with a power law of ~0.3-0.5 and the diffusion was found to belong to the family of fractional Brownian motion anomalous diffusion.

We rationalized that the source of the viscoelasticity is a protein that can temporarily bind chromatin. We identified one source protein (lamin A) that dramatically affects the diffusion pattern and leads to a phase transition from viscoelastic to viscous diffusion when its expression is inhibited. We suggest a rather simple mechanism that explains the organization maintenance of the chromosomal territories. It is based on the properties of the DNA itself organized by cross-links of lamin A and mediated by other proteins.

 
Amit Keren, Faculty of Physics, Technion
19/10/2015 - 10:30

In this talk I will present progress in the use of high energy particles, produced at accelerators or reactors, to address problems in solid state physics. In particular I will review advances in neutron scattering, muon spin resonance, and Resonance Elastic and Inelastic X-ray spectroscopy. I will provide examples from the field of high temperature superconductivity.

Edward Bormashenko
22/06/2015 - 10:30 - 12:00

Self-propulsion of liquid marbles filled with aqueous alcohol solutions and placed on a water surface is reported. The characteristic of velocity of the marbles is ca. 0.1 m/s. The phenomenon of self-propulsion is related to the Marangoni solutocapillary flow caused by the condensation of alcohol, evaporated from the liquid marble, on a water surface. The Marangoni flow in turn enhances the evaporation of alcohol from marbles. Addition of alcohol to the water supporting the marbles suppresses the self-propulsion. The propulsion of liquid marbles is mainly stopped by water drag. The velocity of the center of mass of marbles grows with the increase of the concentration of alcohol in a marble. The velocity of marbles’ self-propulsion is independent on their volume. Impact of external fields on the self-propulsion is discussed.

Host: Eli Sloutskin, Physics Department (phone. 03 - 738 4506; cell. 054 - 393 8246)
Those of you who may be interested in talking with Prof. Bormashenko should mail me (eli.sloutskin@biu.ac.il), listing their preferred time.

 

 

Prof. Efi Efrati, Dept. of Physics, Weizmann Institute
15/06/2015 - 10:30

Handed phenomena are of central importance in fields ranging from biological self-assembly to the design of optical meta-materials. The definition of chirality (Greek for handedness), as given by Kelvin, associates it with the lack of mirror symmetry: the inability to superpose an object on its mirror image. While this definition has guided the classification of chiral objects for over a century, the quantification of handed phenomena based on this definition has proven elusive, if not impossible as manifest in the paradox of chiral connectedness. In this talk I will put forward a quantification schemein which the handedness of an object depends on the direction in which it is viewed and thus best quantified by a pseudo-tensor. While consistent with familiar chiral notions, such as the right hand rule, this framework allows objects to be simultaneously right and left handed. The trace of the suggested handedness tensors recover Kelvin's definition, yet their full structure is richer, and proven to be in quantitative agreement with the direction-dependent handed behavior of phenomena ranging from fluid flow to optical activity. I will review specific examples of handedness tensors, and discuss how the tensorial approach resolves the existing paradoxes and naturally enables the design of handed meta materials from symmetry principles.

Nadav Katz, HUJI
08/06/2015 - 10:30

Superconducting devices, containing Josephson junctions and resonant structures, are at the forefront of quantum information science today. These devices, built with various  nanofabrication  techniques  and  resulting  in  tunable  and  highly  nonlinear  resonances, uncover  also exciting  physics  of  the  superconducting  state  and surrounding  dielectric  and  magnetic  environment.  I  will  review  some  of  the recent progress in  the  field  and  present  some  of  our  results on both quantum optical control and subsequent metrology of two-level  defect  states and magnetic flux noise in the environment. 
 

Prof. Robin Selinger, Kent State University
18/05/2015 - 10:30

We explore novel mechanisms of pattern formation in soft matter, examining why a lipid membrane crumples during a phase transition and how stimuli-responsive liquid crystal polymer films can be patterned to induce programmed shape transformations . In both of these materials, whose constituent molecules align to form orientationally ordered phases, topological defects play a key role: they drive changes in morphology by inducing curvature. In lipid membranes cooled through a phase transition into the tilted “gel” phase, we theorize that defects nucleate spontaneously and then coarsen via kinetic competition between defect pair-annihilation and membrane shape evolution. We explore this process via simulation using a coarse-grained model and also study membranes with nematic order. Next we examine the role of defects in stimuli-responsive liquid crystal polymers, which flex when exposed to light or a change of temperature. If a precise pattern of defects is induced in the sample when it is cross-linked, a process known as “blueprinting,” then under stimulus an initially flat film will twist, curl, or fold into a complex shape, a form of programmed auto-origami. We use 3-d nonlinear finite element simulation studies to explore the mechanism by which the complete trajectory of motion is encoded in the sample’s nematic director field, and compare with relevant experiments. 

Prof. Issai Shlimal, BIU
11/05/2015 - 10:30

The phenomenal mechanical, thermal, electrical and optical properties discovered in recent years from the first true two-dimensional material - monolayer graphene have attracted the tremendous enthusiasm because of possible graphene-based device application. In this sense, the influence of disorder is interesting due to possibility of obtaining a high-resistance state, which is important for application in electronics. In the experiment, disorder in graphene is introduced in various ways: by oxidation, hydrogenation, chemical doping, as well as irradiation by different ions with different energies. The advantage of the latter method consists in an accuracy and reproducibility of the process and ability to anneal the radiation damage.

In this talk, I will make an introduction into the subject, followed by presentation of the results of investigation of the properties of monolayer graphene samples gradually disordered by ion bombardment. To probe the evolution of disorder, the Raman spectroscopy (RS) and resistance measurements were used. The main new results of this work consist in (i) observation of the utmost degree of disorder, when graphene, due to high density of defects, is no longer continuous film but split into separate fragments; (ii) observation of the correlation between intensity of RS lines and sample resistance: transition from the low-defect to the high-defect density regime occurs at the resistance equal to reciprocal value of the minimal graphene conductivity. (iii) observation of gradual change in the mechanism of electron transport from metallic conductivity in the initial pristine films to the regime of weak localization-weak antilocalization in the weakly disordered samples and finally to the variable-range hopping conductivity of localized carriers in strongly disordered graphene.

Prof. Aviad Frydman, BIU
04/05/2015 - 10:30

The 2013 Nobel Prize in physics was awarded to Peter Higgs and Francois Englert "for the theoretical discovery of the mechanism that contributes to our understanding of the origin of mass of subatomic particles". This Nobel committee decision was based on the detection of the predicted "Higgs boson" in the CERN Large Hydron Collider within the framework of the largest experiment ever held by mankind. Obviously, this recent discovery regarding the "God Particle" generated much worldwide interest. But what is less known is that the inspiration for its prediction came from theoretical works in the field of Superconductivity. 

Ironically, while the ideas regarding this ‘missing link’ in the Standard Model of elementary particles were stimulated by superconductor theory, the Higgs mode was never clearly observed in superconductors. The main reason for this is the fact that the energy required to excite the Higgs boson, the Higgs mass, is large enough to break cooper-pairs and hence suppress superconductivity.  Nevertheless, recent theories show that if the Higgs mass could be softened below the superconducting gap it should be visible in two dimensions. Such conditions can be met by tuning a superconducting film towards a superconductor-insulator quantum phase transition. Indeed, in our experimental study on thin superconducting films for which the superconductor to insulator transition is tuned by disorder, an excess optical spectral weight below the superconducting gap energy was observed and identified as an explicit observation of the Higgs mode in a superconductor. 

This experiment closes a historical circle by connecting the Higgs Boson to its theoretical "ancestor" and serves as a beautiful example that the same fundamental physics can govern in two disparate systems (elementary particles and conventional superconductors) for which the energy scales differ by 15 orders of magnitude.

 

Prof. Dan Shahar
27/04/2015 - 10:30

We show that, at low temperatures (T<0.2 K), Copper-pairs undergoing localization transition become decoupled from the host-material phonons. This allows us to experimentally study an interacting, many-body, quantum system far from equilibrium. Our system exhibits complex dynamics alongside a new second-order phase transition.

Beena Kalisky, BIU
20/04/2015 - 10:30

Complex oxide materials have a broad range of functionality such as ferromagnetism,piezoelectricity, and superconductivity. When combinations of complex oxides are grown as heterostructures, changes in the local electronic-structure at the interface can create new electronic phases that cannot exist in either parent material. One example is the interface formed by growing LAO on STO. Though both materials are non magnetic insulators, the interface between them shows conductivity, superconductivity and even magnetism. 

In the LAO/STO system we found nanoscale patches of magnetism coexisting with superconductivity. I will describe our efforts to understand this magnetism, by mapping the landscape of ferromagnetism, superconductivity and conductivity with scanning SUQID microscopy. I will focus on viewing the local distribution of current flow at the interface, where we found that the current flow is enhanced on conductive channels that are related to STO tetragonal domain structure. The interplay between substrate domains and the interface provides an additional mechanism for understanding and controlling the behaviors of heterostructures.

Lazar Friedland, Hebrew University of Jerusalem
13/04/2015 - 10:30

Autoresonance is a fascinating phenomenon of nonlinear physics, where a perturbed nonlinear system is captured into resonance and stays phase-locked with perturbing oscillations (or waves) continuously despite variation of system's parameters. The persistent phase-locking means excursion in system's solutions space and frequent emergence of nontrivial coherent structures. For nearly half a century (starting from Veksler and McMillan in 1945) studies of autoresonance were limited to relativistic particle accelerators and microwave sources, but many new applications of the autoresonance idea emerged since 1990 in atomic physics, nonlinear dynamics, nonlinear waves, plasmas, fluid dynamics, and, most recently, superconducting Josephson junctions. 

The salient feature of autoresonance is the existence of a sharp threshold on the amplitude of the chirped frequency driving perturbation for autoresonant transition. In this talk I will discuss the effects of thermal noise and quantum fluctuations on the threshold. I will also address the quantum counterpart of the of the classical autoresonance phenomenon, i.e. the quantum ladder climbing and the continuous transition between these two regimes.

Prof. Francoise Remacle
23/03/2015 - 10:30

The recent developments in the generation of optical attopulses suggest that it will soon become experimentally feasible to induce and subsequently directly probe ultrafast charge transfer between the end moieties of the modular molecule. One ultrafast pulse creates a non-stationary state of the neutral or of the cation and a second one ionizes it. Such experiments would allow characterizing a purely electronic time scale, before the coupling to the nuclei takes place. This is a pre Born-Oppenheimer regime where the electronic states are not stationary.[1]

We will report on the simulation of realistic pump probe experiments that monitor the ultrafast electronic dynamics in LiH,[2,3] in the medium size bifunctional molecule PENNA (C10H15N)[4] (Fig.1), C60 and other medium size molecules using a coupled equation scheme that includes the ionization continua and field effects. We show that in a short IR pump- XUV attosecond pulse train (APT) scheme that the APT can be used to disentangle the coherent superposition of states built by the IR pump pulse, acting as frequency filter.[2] The density motion between the two ends of a molecular system is probed by the anisotropy ionization parameter computed as the normalized difference between the ionization yields at the two moieties.[4] Heatmaps of the ionization anisotropy parameter as a function of the delay time between the two pulses and the kinetic energy of the photoelectron exhibit oscillations that reflect the beating periods of the electron density. 

References

[1] F. Remacle and R. D. Levine Proc. Natl. Acad. Sci. USA 2006, 103, 6793-6798.

[2] B. Mignolet, R. D. Levine, F. Remacle Phys. Rev. A 2014, 88, 021403(R).

[3] B. Mignolet, R. D. Levine and F. Remacle, J. Phys. Chem A 2014, 118 ,6721-6729.

[4] B. Mignolet, R. D. Levine, F. Remacle J. Phys. B 2014, J. Phys. B: 47, 124011.

Prof. Tatyana I. Baturina
16/03/2015 - 10:30

For nearly a half century the dominant orthodoxy has been that the only effect of Cooper pairing is a state with zero resistivity at finite temperatures, superconductivity.  In this talk I will show that Cooper pairing can generate a dual state with zero conductivity in a finite temperature range, superinsulation.  Superconductor-superinsulator duality rests on the symmetry of the Heisenberg uncertainty principle relating the amplitude and phase of the superconducting order parameter. It is realized in the critical region of the quantum superconductor-insulator transition (SIT) in two-dimensional systems via the duality between the vortex and charge of the Berezinskii–Kosterlitz–Thouless transition. I will discuss the origin of the long-range logarithmic two-dimensional Coulomb forces between the charges ensuring the vortex-charge duality in the critical vicinity of the SIT.

Prof. Baturina is from A. V. Rzhanov Institute of Semiconductor Physics SB RAS, 13 Lavrentjev Avenue, Novosibirsk, 630090 Russia

 

Prof. Jörg Langowski, Biophysics of Macromolecules, DKFZ Heidelberg, Germany
09/03/2015 - 10:30

Proteins acting on DNA need to penetrate a dense network of chromatin and associated macromolecules in the cell nucleus to access their target sites. Intracellular mobility of proteins is characterized by diffusion coefficients of the order of 1-100 μm2/s, leading to millisecond time scales for movement on the submicrometer scale.
Typical microscopic methods used for characterizing intracellular protein mobility are, e.g., fluorescence photobleaching recovery (FRAP) and fluorescence correlation spectroscopy (FCS). Of these, FRAP can image protein mobility in entire two-dimensional sections of live cells, but is typically limited to the time resolution of confocal image series, some frames per second. FCS, on the other hand, has fast time resolution but so far has been limited to single-point measurements in the focus of a laser beam, or to techniques that utilize the inherent time structure of confocal scans. In my seminar I will show results from single plane illumination microscopy based fluorescence correlation spectroscopy (SPIM-FCS), a new method that combines the fast time resolution of FCS with the ac- quisition of mobility data in parallel on an entire two-dimensional cross-section. This provides diffusion coefficients, flow velocities, concentrations and interactions as imaging parameters.
 

Benjamin Lev
26/01/2015 - 10:30 - 12:00
Microscopy techniques co-opted from nonlinear optics and high energy physics have complemented solid-state probes in elucidating exotic order manifest in condensed matter materials.  Up until now, however, no attempts have been made to use modern techniques of ultracold atomic physics to directly explore properties of strongly correlated or topologically protected materials.  Our talk will present the SQCRAMscope, a novel Scanning Quantum CRyogenic Atom Microscope technique for imaging magnetic and electric fields near cryogenically cooled materials.  With our SQCRAMscope, we aim to image inhomogeneous transport and domain percolation in technologically relevant materials whose order has evaded elucidation.
 
 
Barak Dayan, WIS
19/01/2015 - 10:30 - 12:00

I will present the recent demonstration of deterministic photon-atom and photon-photon interactions using a single atom coupled to a chip-based micro-resonator. Based on passive, interference-based nonlinearity which leads to deterministic single-photon Raman passage (DSPR), this scheme swaps the quantum states of a single photon and a single quantum emitter (a 87Rb atom, in our case), with no need for any control fields.
Beyond the ability to route single photons by single photons, this scheme can also function as a quantum memory and a photonic universal quantum gate. It can therefore provide a building block for scalable quantum networks based on completely passive nodes interconnected and activated solely by single photons.

Ref:

[1] D. Pinotsi & A. Imamoglu, Phys. Rev. Lett. 100, 093603 (2008)

[2] G. Lin, X. Zou, X. Lin, and G. Guo, Europhysics Letters 86, 30006 (2009)

[5] K. Koshino, S. Ishizaka & Y. Nakamura, Phys. Rev. A 82, 010301(R) (2010)

[4] S. Rosenblum, A.S. Parkins & B. Dayan, Phys. Rev. A 84, 033854 (2011)

[5] I. Shomroni, S. Rosenblum, Y. Lovsky, O. Bechler, G. Guendelman & B. Dayan, Science 345, 903 (2014)

[6] S. Rosenblum & B. Dayan, “Analysis of Photonic Quantum Nodes Based onDeterministic Single-Photon Raman Passage”, arXiv: quant-ph 1412.0604 (2014) )

 
Prof. Giacomo Ghiringhelli
12/01/2015 - 10:30

The appearance of superconductivity (SC) in layered cuprates upon doping with holes or electrons is still the matter of intense debate almost 30 years after the discovery of the so-called high Tc superconductors (HTcS). Given the strong superexchange interaction that stabilizes a 2D square lattice antiferromagnetic (AF) order in the parent compounds, the actual evolution of the spin order and its possible coupling to charge instabilities have been questioned and extensively studied over the years. In fact magnetic and/or charge fluctuations might play a central role in the superconductive transition. Moreover their possible relation with the pseudogap and the Fermi surface shape and size is still questioned. Working at the ESRF and SLS [1], in the last 10 years we have developed high resolution resonant inelastic x-ray scattering (RIXS) and used it at the Cu L3 edge of HTcS. This technique is the only alternative to inelastic neutron scattering for the study of magnons and paramagnons in those materials [2,3]. RIXS has revealed that spin excitations persist up to very high doping levels, both in hole- and electron-doped compounds [4,5]. The doping dependence of those magnetic excitations and their inherent character (spin-wave-like rather than Stoner mode) has been extensively characterized in several cuprate families. Moreover the energy selectivity allowed us to discover the reflection peak associated to charge density modulations, initially in underdoped YBCO [6] and, more recently, in optimally doped Bi2212 [7], LSCO and NdBCO. The evidence of persistent short range spin correlation and of ubiquitous charge density fluctuations in cuprates provided by R(I)XS has drastically reopened the debate over the basic mechanisms of HTcS. Finally, the new opportunities in terms of energy resolution, sample orientation control and detection efficiency to be provided by the forthcoming ID32-ERIXS facility at the ESRF and the perspective opened by time-resolved RIXS at the European XFEL will be discussed.

Eli Barkai
05/01/2015 - 10:30 - 12:00

Fractional calculus is an old branch of mathematics which deals with fractional order derivatives. Recently the Davidson's group (Weizmann) has recorded the spatial diffusion of cold atoms in optical lattices, fitting the results to the solution of a fractional diffusion equation. Within the semi classical theory of Sisyphus cooling we derive this fractional equation and discuss its meaning and its limitations [1,2]. An asymptotically weak friction force, induced by the laser field, is responsible for the large deviations from normal transport theory (and from Boltzmann-Gibbs equilibrium concepts [3]) at least below a critical value of the depth of the optical lattice.

1. E. Barkai, E. Aghion, and D. Kessler From the area under the Bessel excursion to anomalous diffusion of cold atoms Physical Review X 4, 021036 (2014)
2. D. A. Kessler, and E. Barkai Theory of fractional-Levy kinetics for cold atoms diffusing in optical lattices Phys. Rev. Lett. 108, 230602 (2012).
3. A. Dechant, D. A. Kessler and E. Barkai Deviations from Boltzmann-Gibbs equilibrium in confined optical lattices arXiv:1412.5402 [cond-mat.stat-mech] (2014).

Dr. Ariel Amir
29/12/2014 - 10:30

Microorganisms such as bacteria and budding yeast are remarkably successful in accurately self-replicating themselves within several tens of minutes. How do cells decide when to divide? How do they control their morphology? I will show how ideas from statistical mechanics and materials science can help answer these questions. In particular, I will show how a stochastic model of cell size control, combined with single cell data, can be used to infer a particular strategy for cell size control in bacteria and budding yeast, and how the theory of elasticity can be utilized to understand the coupling of mechanical stresses and cell wall growth in bacteria

Prof. Gal Kaminka, Department of Computer Science and Brain Science Research Center, BIU
15/12/2014 - 10:30

This informal talk will survey recent advances in robotics and artificial intelligence research, worldwide, and specifically at Bar Ilan University's computer science department. It will present the quiet commercial and scientific revolution enabled by these advances, and introduce little-known, but common challenges, opportunities, and surprises. The talk will highlight milestone achievements in the 12 years since robots firstcame to Bar Ilan, and discuss open challenges that may be of particular interest to physicists:  phase transitions in computational problems; a possible relationship between crowds, magnetism, and social psychology; Asimov's vision of prediction technology (psychohistory), and programmable nano-scale robots. The talk assumes no prior knowledge of computer science or robotics.

Dr. Hagai Perets
08/12/2014 - 10:30

The wide diversity of cosmic explosion arise from a variety of complex physical phenomena.  Each one of these cosmic fireworks, be it supernovae, gamma ray burst, stellar collisions or tidal disruptions, is different in nature, but many of them also share many similarities. The study of such explosions had reshaped  science over and over again for thousands of years, breaking the most basic scientific paradigms, building new ones and shedding new light on our understanding of the origin of the universe, its evolution and constituents. I will review the history of supernova research and its breakthroughs and then focus on some of the frontier science done on peculiar types of supernovae discovered in recent years, ranging in orders of magnitude in brightness and time-length. I will discuss the strongly debated progenitors of such cosmic explosions, the main processes involved in their actual production, and their major implications for the evolution of the universe, and I will touch upon the many open questions which they raise. In particular, I will explain how the regular seemingly delicate but shining life of stars eventually leads to their violent explosive death;  how close symbiotic relations between companion stars which exchange materials between them end up in a blasting breakout of a ball of fire, and how all of these can explain our own origins.

Prof. Emanuele Dala Tore, Department of Physics, BIU
01/12/2014 - 10:30

Depicted by P. W. Anderson as "more is different", an emergent phenomenon occurs when a large number of identical objects behaves differently than its original constituents. This situation lays at the core of our understanding of strongly correlated materials, such as insulators and superconductors. However, present theories are often limited to equilibrium systems that can be described by a thermal ensemble at a fixed temperature. How can we extend these ideas to non-equilibrium environments? I will describe a recent approach to the problem, where the temperature is represented as an emergent phenomenon. Although the microscopic degrees of freedom are externally driven and do not equilibrate, the macroscopic properties of the system often display a thermal behavior. Starting from specific case studies, I will present successes and failures of this approach. In my last slide, I will discuss possible relations with the philosophical concept of the messianic era as an emergent property of the universe.

Prof. Igal Szleifer, Departments of Chemistry and Biomedical Engineering, Northwestern University
24/11/2014 - 10:30

The development of synthetic materials for biorelated applications requires exquisite control of the physical and chemical environment within the materials. In biological systems, mucus represents a family of hydrogels that are responsive to the environment, in particular the pH. In this talk we will discuss pH within synthetic and biological hydrogels. We will start by properly defining the pH in the thermodynamic sense and in terms of the common use of the term. Then, we answer the question what is the pH within a hydrogel and how it relates to the conditions in which it is synthesized and stored. The physical and chemical properties of pH-responsive gels are found to depend on the coupling between acid-base equilibrium, molecular organization and physical interactions. For example, the network’s degree of protonation is not only determined by chemical composition of the bath solution but also by the ability of the polymeric structure to modify the local environment. This coupling results in swelling (or shrinking) that depends on the bath pH and salt concentration. We will discuss examples of different types of hydrogels. For example in bulk systems we predict that the gel pH can be several units smaller than the bath pH depending on the salt concentration. In thin films we will discuss the gradients of protonation state and pH that results from the inhomogeneous distribution of species within the film and how this effect has implications on the effective interactions between proteins (and nanoparticles) and the film. The role of pH and ionic strength on protein adsorption and its implications to chromatography will be discussed. The theoretical predictions can be used as guidelines for the design of responsive gels in a variety of applications ranging from drug delivery systems to tissue engineering scaffolds and they provide for fundamental understanding on the non-trivial behavior of these gels. Moreover, our predictions demonstrate that the chemical state within soft materials may be dramatically different from that of the environment solutions in contact with them. We find than in systems where molecular organization, chemical equilibrium and physical interactions are coupled the behavior of the system is very different from the sum of the parts that form it.

Prof. Dirk Schwalm
17/11/2014 - 10:30

Since the formulation of Special Relativity by Albert Einstein more than 100 years, its main ingredient, the space-time symmetry of local Lorentz invariance (LI), forms one of the corner stones of all currently accepted theories describing nature on a fundamental level. Already this fundamental role alone demands thorough experimental affirmation of this symmetry. Further motivation for incessant experimental tests with ever increasing scrutiny comes from theoretical attempts to solve some of the unsettled problems in contemporary physics, such as the reconciliation of quantum theory and general relativity, which allow LI to be violated.   

Within the wealth of LI tests, ‘Ives-Stilwell’ experiments stand out for their large Lorentz boost, which neither depend on sidereal variations nor on a special reference frame. These experiments, which are based on the optical Doppler effect, directly determine the relativistic time dilation effect, one of the most fascinating and at the same time most disconcerting aspects of the space-time symmetry of Special Relativity as it abolishes the notion of absolute time. I will report on our modern versions of this experiment, which involves metastable 7Li+ ions moving with velocities of up to 1/3 of the velocity of light as atomic clocks. The experiments combine ion storage and ion cooling in heavy ion storage rings together with laser induced saturation and optical-optical double resonance spectroscopy to read out the clock frequencies.  Comparing these frequencies with those measured at rest allowed us to verify the relativistic time dilation with unprecedented precision.  

Edvardas Narevicius
10/11/2014 - 10:30
There has been a long-standing quest to observe chemical reactions at low temperatures where reaction rates and pathways are governed by quantum mechanical effects or long range interactions. This field of Quantum Chemistry has been dominated, to date, by theory, with almost no experiments. The difficulty so far, has been to realize low enough collisional velocities between neutral reactants, so that the de Broglie wavelength becomes long enough for the quantum wave nature to emerge as a dominating effect. We will discuss how reaction temperatures on the order of several milli Kelvin can be achieved without laser cooling by merging cold and fast molecular and atomic beams. We will show that by controlling the initial electronic state of metastable helium in the ionisation reactions with molecules we can switch reaction mechanism from the universal Langevin behavior into the quantum tunnelling dominated regime.
 
1. A. B. Henson, S. Gersten, Y. Shagam, J. Narevicius, E. Narevicius, "Observation of Resonances in Penning Ionization Reactions at Sub-Kelvin Temperatures in Merged Beams", Science 338, 234, 2012
2. E. Lavert-Ofir, Y. Shagam, A. B. Henson, S. Gersten, J. Klos, P. S. Zuchowski, J. Narevicius and E. Narevicius, "Observation of the isotope effect in sub-kelvin reactions", Nature Chemistry 6 (4), 332-335, 2014 
Prof. Baruch Meerson, Racah Institute of Physics, Hebrew University
03/11/2014 - 10:30

In 1917 von Smoluchowski suggested a simple-minded model of diffusion-controlled binary   
reactions. It consists of an immobile spherical trap of radius R surrounded by a gas of Brownian

particles. The particle flux into the trap mimics the rate of diffusion-controlled reactions. Since

its inception, the Smoluchowski model and its extensions inspired multitudes of studies. The vast

majority of them continued to assume that the particles do not interact with other. Here we extend

this model to a whole class of diffusive gases of interacting particles. Employing the Macroscopic

Fluctuation Theory, we evaluate the probability P(T) that no gas particle hits the trap until a

long but finite time T. We also find the most likely density history of the gas conditional on the

non-hitting. The results crucially depend on the dimension of space d and on the rescaled parameter

  l = R/√D0T where D0 is the gas diffusivity.

Zohar Komargodski
27/10/2014 - 10:30 - 11:30

I will review several recent advances in Particle Physics and Quantum Field Theory. The emphasis is on concepts which are applicable beyond perturbation theory. For example, we will discuss the  Entanglement Entropy of the vacuum, the number of light excitations, the relation to gravity, and the symmetries of Quantum Field Theory.

 

Prof. Daniel Stein, Depts. of Physics and Mathematics, NYU
20/10/2014 - 10:30

One of the deepest scientific questions we can ask is, How might complexity arise? That is, starting from simple, undirected processes subject to physical and chemical laws, how could structures with complex shapes and patterns arise, and even more perplexing, what processes could give rise to living cells, and how might they then organize themselves into complex organisms, leading ultimately to such things as brains, consciousness, and societies? We are far from answering these questions at almost any level, but they have attracted increasing attention in the scientific community, and some initial headway has been made. The basic problem can be reframed as one involving the self-organization of microscopic constituents into larger assemblies, in such a way that the process leads to an increase of information, the creation of new patterns, and eventually increasing hierarchical levels of complex structure. The key to understanding these processes cannot be found in any single (natural or social) scientific field but rather in collaborations that cross many disciplinary boundaries. Although we are still at the initial stages of inquiry, new and interesting approaches and points of view have arisen. In this talk I present one that arises from the point of view of physics. We start by describing the (well-understood) phenomenon of matter organizing itself into simple ordered structures, like crystals and magnets, and then explore how our ideas are affected when we consider the effects of randomness and disorder, pervasive in the physical world. We will see that randomness and disorder are, paradoxically, essential for more ordered, complex structures to arise. Using these ideas, we provide some hints (but only hints) as to how we can gain a handle on issues related to the increase of complexity. Underlying all of our considerations is the notion of symmetry in physics: where it comes from and how matter "breaks" its inherent symmetry to create new information and ever-increasing complexity.

Prof. Daniel Podolsky, Department of Physics, Technion
16/06/2014 - 10:30

The Higgs mode is a ubiquitous collective excitation in condensed matter systems with broken continuous symmetry.  It plays a role analogous to the Higgs boson in particle physics.  Its detection is a valuable test of the corresponding field theory, and its mass gap measures the proximity to a quantum critical point. However, since the Higgs mode can decay into low energy Goldstone modes, its experimental visibility has been questioned. In this talk, I will show that the visibility of the Higgs mode depends on the symmetry of the measured susceptibility. I will also present an analysis of the evolution of the Higgs mode upon approach to the Wilson-Fisher fixed point in 2+1 dimensions and demonstrate that the Higgs mode survives as a universal resonance in the scalar susceptibility arbitrarily close to the quantum critical point. I will discuss the implications of these results for experiments on lattice Bose condensates and thin film superconductors near the Mott insulator to superfluid transition.

Prof. Yoav Soen, Dept. of Biological Chemistry, Weizmann Institute
09/06/2014 - 10:30

The development of organisms must be robust enough to maintain adaptive patterns and flexible enough to enable coping with fluctuating external and internal conditions (e.g. environmental, genetic, epigenetic and symbiotic perturbations). How this tension between stability and flexibility is handled and the potential implications of this co-existence to establishment of new adaptations are not clear.

We are addressing these questions by studying stress-induced induction and inheritance of altered developmental patterns in flies. We identified epigenetic and symbiotic-mediated mechanisms which promote increased developmental flexibility under stress and contribute to non-Mendelian transfer of influences across generations.

I will present these findings and discuss their potential implications for bridging ecological and evolutionary processes.

Prof. Uri Sivan, Dept. of Physics, Technion
02/06/2014 - 10:30

Hofmeister and his PhD student, Lewith, discovered 126 years ago that different ions destabilize proteins to a markedly different extent. They ranked ions according to their precipitation power in a series known today as the Hofmeister series. Since then, scientists discovered dozens of additional ion-specific phenomena including surface tension, ion transport through biological and inanimate membranes and channels, colloidal stability, enzyme activity, bacterial growth, and more. Remarkably, with only few exceptions, the same Hofmeister series was discovered to characterize the effect of ions on this myriad of ostensibly different phenomena, strongly suggesting the existence of an underlying common microscopic mechanism. The universality reflected in the Hofmeister series has turned this problem into one of the fundamental puzzles in biophysics and the physics of soft matter. The search for an underlying mechanism has motivated extensive research and important discoveries but the Hofmeister universality proved more challenging than naively anticipated.

In the past few years, our lab has been employing Atomic Force Spectroscopy to measure the effect of different ions on the short range force acting between two surfaces in solution. The full force vs. distance curves obtained this way gave significant new insight into the Hofmeister puzzle and suggested, in combination with recent optical measurements, a surprisingly simple picture of the underlying physics. 

Prof. Lucio Frydman, Department of Chemical Physics, Weizmann Institute
19/05/2014 - 10:30

Magnetic resonance provides a prime tool for elucidating molecular structures in its spectroscopic (NMR) mode, and for the non-invasive mapping of objects in its imaging (MRI) mode. While entailing very different applications, the basic quantum foundations of both NMR and MRI are common. So are many of the techniques used in either molecular elucidations and/or images –and foremost among these the Nobel-winning proposition of multidimensional NMR/MRI. While these acquisitions take order-of-magnitude longer acquisition times than 1D traces, we have recently developed a scheme enabling the acquisition of arbitrary multidimensional NMR spectra and/or images (MRI) within a single scan.  This is by contrast to the hundreds or thousands of scans that are usually needed to collect this kind of data. Provided that the target molecule's signal is sufficiently strong, the acquisition time of NMR/MRI scans can thus be shortened by several orders of magnitude.  This new “ultrafast” methodology is compatible with existing multidimensional pulse sequences and can be implemented using conventional hardware. The manner by which the spatiotemporal encoding of the NMR interactions —which is the new physical principle underlying these new protocols— proceeds in these experiments, will be summarized. The new horizons that are opened by these protocols will also be exemplified with a variety of NMR and MRI projects we are currently involved in in fields of chemistry, biophysics, biology and medicine. 

Prof. Javier Tejada, Department of Physics, University of Barcelona
12/05/2014 - 10:30

In my talk I will review the experimental work done in the field of nanomagnets, emphasizing the description of quantum relaxation in magnetic nanoparticles and resonant spin tunneling in molecular magnets. I will start introducing the concepts of both exchange energy and magnetic anisotropy and the static and dynamic magnetic properties of nanoparticles. Then I will move to comment on the effect of quantum tunneling of magnetic poles in magnetic nanoparticles; quantum magnetic relaxation  and the so called quantum resonant spin tunneling.  The next step will be to explain phenomena related to spin tunneling such as quantum magnetic deflagration, the emission of superradiance by the magnetic flame and the possible use of nanomagnets as qubits. To finish, I will comment on the appearance of a new force of quantum origin in molecular magnets.

 

 

Professor Xavier Darzacq, Institute of Biology, ENS Paris
28/04/2014 - 10:30

While membranes do not compartmentalise the nucleus, it shows a complex organisation at many scales. Spatial organisation of chromatin and transcription factors can modulate nuclear functions and in order to study this relation, we have developed methods to localise proteins and mRNAs at the single molecule level and with spatial resolutions in the range of a few nanometers (modifications and improvements of PALM, sptPALM and STORM using adaptive optics). Moreover, proteins move throughout the nucleus by diffusion, transiently and repetitively contacting their target sites. While DNA has been reported as a guide facilitating target search in the cell by restricting 3 dimensional explorations to a 1 dimensional search, such exploration modes were not envisioned mediated by protein-protein interactions. I will discuss chromatin and RNA polymerase II organisation in the nucleus as well as mechanisms guiding proteins to their targets in the nucleoplasm. 

Prof. Azriel Genack, Department of Physics, Queens Colledge, CUNY
07/04/2014 - 10:30

We find a single expression for the average intensity profile of eigenchannels of the transmission matrix inside single and multichannel random media for quasi-ballistic, diffusive and localized waves. The intensity profiles are built upon the simple form of the completely transmissive channel and depend only upon the transmission eigenvalue, τ, the sample length and the localization length. We show that eigenchannel intensity profiles are related to the auxiliary localization lengths introduced by Dorokhov to parameterize τ. The integral of the spatial intensity distribution over the sample volume for unity incident flux , which is the contribution of each eigenchannel to the density of states (DOS), is equal to the derivative of the average phase of the transmission eigenchannel with angular frequency of the incident radiation. The sum of the eigenchannel DOS over all eigenchannels gives the density of states (DOS) which controls spontaneous and stimulated emission and wave localization. This is demonstrated in microwave experiments in the equivalence of spectra of the DOS determined from a decomposition of the wave into transmission eigenchannels and quasi-normal modes.

Prof. Itamar Procaccia, Dept. of Chemical Physics, Weizmann Institute
31/03/2014 - 10:30
We discuss a model metallic glass in which Barkhausen Noise can be studied in exquisite detail, free of thermal effects and of the rate of ramping of the magnetic field. The mechanism of the jumps in magnetic moment that cause the Barkhausen Noise can be fully understood as consecutive instabilities where an eigenvalue of the Hessian matrix hits zero, leading to a magnetization jump $\Delta m$ which is simultaneous with a stress and energy changes $\Delta \sigma$ and $\Delta U$ respectively. Contrary to common belief we find no ``movements of magnetic domain boundaries" across pinning sites, no fractal domains, no self-organized criticality and no exact scaling behaviour. We present a careful analysis of the statistical properties of the phenomenon, and show that with every care taken this analysis is tricky, and easily misleading. Without a guiding theory it is almost impossible to get the right answer for the statistic of Barkhausen Noise. We therefore present an analytic theory, showing that the probability distribution function (pdf) of Barkhausen Noise is not a power law times an exponential cutoff. On the basis of the theory we explain why standard methods to extract the form of the pdf are likely to fail, as indeed happened until now.
Prof. Ehud Altman, Department of Physics of Condensed Matter, Weizmann Institute of Science
24/03/2014 - 10:30

It has been argued recently that, through a phenomenon of many-body localization, closed quantum systems subject to sufficiently strong disorder would fail to thermalize. In this talk I will discuss the nature of the dynamics in the localized state. I will show that rather than being a dead state, the localized phase supports highly non trivial modes of quantum dynamics. Most spectacularly, many-body localization can facilitate the existence of topological order in the entire many-body spectrum rather than in the ground state alone. I will demonstrate with a concrete model of a quantum magnet how this leads to protected quantum-bits that retain perfect coherence even when the system is at arbitrarily high energy.

Prof. Eran Segal, Dept. of Mathematics and Computer Science, Weizmann Institute
10/03/2014 - 10:30

Much of the phenotypic differences among people is attributable to genetic variation in regulatory regions that affect the activity levels of the various genes. However, without a ‘regulatory code’ that informs us how DNA sequences determine gene activity levels, we cannot predict which sequence changes will affect gene activity levels, by how much, and by what mechanism. To address this challenge, we developed a high-throughput method for constructing libraries of thousands of fully designed regulatory sequences and measuring their gene activity levels in parallel, within a single experiment, and with an accuracy similar to that obtained when each sequence is constructed and measured individually. Using this ~1000-fold increase in the scale with which we can study the effect of sequence on gene activity, we designed and measured the activity levels of libraries in which we systematically perturbed different sequence elements. Our results provide several new insights into principles of gene activity regulation, bringing us closer towards a mechanistic and quantitative understanding of how gene activity levels are encoded in DNA sequence.

Prof. Chris H. Greene, Department of Physics, Purdue University, IN, USA
03/03/2014 - 10:30

This colloquium will discuss some of the nonperturbative
physics that occurs when a few particles interact strongly, stressing
low-energy phenomena where one needs to go beyond perturbation theory.
Some of the problems of recent interest include the recombination of 3
or 4 or even 5 ultracold atoms to form molecules, a key process that
tends to eject atoms and cause losses from a Bose-Einstein condensate.
Resonances in this system are connected with the intriguing Efimov
effect.  Another recent interest has been the field of artificial gauge
potentials in cold atom physics, where an appropriate laser dressing of
neutral atoms causes them to behave as though they were charged
particles in a magnetic field or even with artificial spin-orbit
coupling.  I will discuss recent developments that allow the theory to
treat such systems quantitatively and also enable qualitative intuition
to be developed, in the context of recent experiments.

Prof. Itzik Ben-Itzhak, Department of Physics, Kansas State University
24/02/2014 - 10:30

We have studied laser-induced fragmentation of molecular-ion beams using coincidence 3D momentum imaging, with direct separation of all the reaction products measured simultaneously. These measurements provide detailed kinetic energy release and angular distributions of the different fragmentation processes. We mainly focus on the fundamental H2+ and H3+ molecules (in 5-50 fs laser pulses having 1012-1016 W/cm2 peak intensity) as models for more complex systems, and at times we do explore more complex molecules such as O2+ and CO2+.

In this talk, we will discuss electron localization on specific nuclei during strong-field dissociation of molecular-ion beams which is controlled by the relative phase between the 790 and 395 nm components of an ultrashort laser pulse.

In addition, clear experimental and theoretical evidence for the intriguing zero-photon dissociation (ZPD) process of H2+ will be presented. The key role of the laser-pulse bandwidth and chirp on ZPD control will be discussed. Moreover, we will explore control over the final dissociation product of HD+, either H+ + D or H + D+ – usually referred to as channel asymmetry.

Prof. Yuval Grossman, Department of Physics, Cornell University, NY USA
13/01/2014 - 10:30
Leptogenesis

There are two open questions in physics which seem
unrelated. The first is why is there only matter around us? The second
is how neutrinos acquire their tiny masses? It turns out that these
two open questions may be related. That is, the same mechanism that
gives neutrino masses can also generate a universe without
anti-matter. In this talk I will explain the connection between these
two issues and describe the on-going theoretical and experimental
efforts in understanding them.

Prof. Frédéric Chevy, Ecole Normale Supérieure, Paris, France
06/01/2014 - 10:30

The understanding of the properties of strongly correlated quantum systems is one of the most challenging open problems in modern physics, since it is relevant to fields as different as condensed matter, astrophysics or nuclear physics. Using the latest techniques of manipulation of ultracold vapors, it is now possible to probe the quantum many body problem using the tools of atomic physics. In this talk, I will show that it is possible to engineer model experimental systems reproducing faithfully some of the most popular hamiltonians used in theoretical physics. I will illustrate this on the study of the thermodynamic properties of strongly correlated gases that can now be benchmarked accurately using advanced experimental and theoretical techniques.

Prof. G.V. Shlyapnikov, LPTMS, Université Paris Sud, Bat. 100, 91405 Orsay, France and University of Amsterdam, The Netherlands
30/12/2013 - 10:30

It is commonly accepted that there are no phase transitions in one-dimensional (1D) systems at a finite temperature, because long-range correlations are destroyed by thermal fluctuations. I will demonstrate that the 1D gas of short-range interacting bosons in the presence of disorder can undergo a finite temperature phase transition between two distinct states: fluid and insulator. None of these states has long-range spatial correlations, but this is a true albeit non-conventional phase transition because transport properties are singular at the transition point. In the fluid phase the mass transport is possible, whereas in the insulator phase it is completely blocked even at finite temperatures. Thus, it is revealed how the interaction between disordered bosons influences their Anderson localization. This key question, first raised for electrons in solids, is now crucial for the studies of atomic bosons where recent experiments have demonstrated Anderson localization. I then consider weakly interacting bosons in a 1D quasiperiodic potential (Aubry-Azbel-Harper model), where all single-particle states are localized if the hopping amplitude in the primary lattice is smaller than half the amplitude of the secondary incommensurate lattice. The interparticle interaction may lead to the many-body localization-delocalization transition, and I will show the finite temperature phase diagram. Counterintuitively, in a wide temperature range an increase in temperature requires a higher interaction strength for delocalization and thus favors the insulator state. In this sense, we have an object that ''gets frozen'' under an increase in temperature.

Prof. Tsevi Mezeh, School of Physics and Astronomy, Tel-Aviv University
23/12/2013 - 10:30

The talk will review the history of the discovery of the
extra-solar planets, with emphasis on the recent findings
Kepler and CoRoT space missions. I will show that we have found
systems that have features different than almost all the
characteristics of our own planetary system.
 

Prof. Tomer Volansky, School of Physics and Astronomy, Tel Aviv University
16/12/2013 - 10:30

The discovery of the Higgs boson at the LHC is one of the greatest scientific achievements this centuries.   Still, despite the anticipation, no unambiguous signal of physics beyond the Standard Model of particle physics has been observed at colliders or at experiments that search for dark matter, to date.   In this talk I will review the current theoretical and experimental state of particle physics, in light of dark matter experiments and the LHC results.  I will then discuss the near future plans in the field and shortly speculate on the various possible outcomes and their implications to particle physics.

Professor Anton Zilman, Department of Physics, Uniersity of Toronto
09/12/2013 - 10:30

Abstract: Nuclear Pore Complex (NPC) is a biological “nano-machine” that controls the  transport between the cell nucleus and the cytoplasm and is involved in a large number of regulatory processes in the cell. It is a remarkable device that combines selectivity with robustness and speed. Unlike many other biological nano-channels, it functions without direct input of metabolic energy and without transitions of the gate from a ‘closed’ to an ‘open’ state during transport. The key, and unique, aspect of transport is the interaction of the cargo-carrying transport factors with the unfolded, natively unstructured proteins that partially occlude the channel of the NPC and its nuclear and cytoplasmic exits. Recently, the Nuclear Pore Complex inspired creation of artificial selective nano-channels that mimic its structure and function for nano-technology applications.

Mechanistic understanding of the transport through the Nuclear Pore Complex, and in particular its selectivity is still lacking. Conformational transitions of the unfolded proteins of the NPC, induced by the transport factors, have been hypothesized to underlie the transport mechanism and its selectivity. These conformational changes are hard to access in vivo; they have been investigated in vitro, generating apparently contradictory results. I will present a theoretical framework that explains the mechanism of selectivity of transport through the NPC and related artificial nano-channels. The theory provides a general physical mechanism for selectivity (even in presence of noise) based on the differences in the interaction strength of the transported molecules with the polymer-like unfolded proteins within the NPC. The theoretical predictions have been verified in experiments with bio-mimetic molecular nano-channels.

Prof. David Gershoni, Department of Physics, Technion
25/11/2013 - 10:30

I will discuss recent  studies of single semiconductor quantum dots as excellent sources of single and entangled photons. In particular I will discuss and demonstrate methods to fully control the spin state of quantum dot confined carriers and to entangle between their spin states and the polarization states of emitted single photons.

Prof. Eshel Ben-Jacob, Dept. of Physics, Tel-Aviv University
18/11/2013 - 10:30

Cancer continues to elude us. Metastasis, relapse and drug resistance are all still poorly understood and clinically insuperable. Evidently, the prevailing paradigms need to be re-examined and out-of-the-box ideas ought to be explored. Drawing upon recent discoveries demonstrating the parallels between collective behaviors of bacteria and cancer, we present a new picture of cancer as a society of smart communicating cells. There is growing evidence that cancer cells, much like bacteria do, rely on advanced communication, social networking and cooperation to grow, spread within the body, colonize new organs, relapse and develop drug resistance. We address the role of communication, cooperation and decision-making during tumoregenesis. This leads to a new picture of cancer cell migration, metastasis colonization and cell fate determination. We reason that the new understanding calls for “cyber war” on cancer – the developments of drugs to target cancer communication and control. 

Prof. Lev Khaykovich
11/11/2013 - 10:30

Few-body systems with resonantly enhanced two-body interactions display universal properties in the sense that they are independent of the details of the short-range interaction potential. The central paradigm in the three-body domain, predicted in the early 1970s by V. Efimov, is associated with the infinite ladder of weakly bound states with discrete scaling invariance. This curious prediction avoided experimental verification in different systems for decades, and only recently and exclusively surrendered to ultracold atoms. After giving a general introduction into Efimov scenario, I will describe the remarkable progress in its experimental investigation with the emphasize to our studies performed with ultracold lithim gas

Prof. Hagai Eisenberg, Racah Institute, HUJI
04/11/2013 - 10:30

The generation of entanglement between more than two particles is a major challenge of all physical realizations. Single photons are one of the most promising realizations of quantum bits (qubits), as they are easily manipulated and preserve their coherence for long times. Quantum information can be stored in many different degrees of freedom of the photons. Only recently, eight photons were entangled in a single state through their polarization degree of freedom. The main difficulties in increasing this number are the elaborated setups required and the low rates of state production. I will present a novel and simple scheme that can in principle generate entanglement between any number of photons from a single setup. Because of some special symmetries of this setup and the fact that it combines photons in different paths as well as from different times, there are some surprising consequences that challenge our understanding of non-locality and the measurement of quantum states. A roadmap for even better photon entanglement sources that are suitable for quantum computation will also be presented.

Prof. Rudolf P. Huebener, Eberhard Karls Universität, Tübingen
28/10/2013 - 10:30

At the end of the 19th century due to the rapid growth of artificial illumination there developed a need for quantitative optical data and relevant standards. Hence, in the optical laboratory of the Physikalisch-Technische Reichsanstalt in Berlin the spectral distribution of the light intensity was measured over a large frequency range. The new data could not be explained in terms of the existing models. Between October and December 1900 Max Planck arrived at his famous radiation law based on Boltzmann’s probabilistic entropy expression. As a key novelty Planck introduced the quantization of the radiation energy in terms of the discrete energy elements hν, with the universal constant h. Whereas Planck did not accept the full impact of the new quantum physics for nearly 10 years, it was Albert Einstein with his light quanta in 1905 and his quantized lattice vibrations in 1906, and a few years later Walther Nernst with his specific heat measurements, who strongly pushed the new ideas about the quantum physics. 

Professor Jeffrey Gordon, Department of Solar Energy and Environmental Physics , Ben-Gurion University
21/10/2013 - 10:30

Recent advances from two diametric approaches for realistically approaching the fundamental limits to solar cell conversion efficiency, which follow from basic thermodynamics, will be presented. One relates to a new concept in cell architecture for concentrator photovoltaics, with the possibility of using exclusively indirect bandgap semiconductors (including Si and Ge) at irradiance values of thousands of suns. The second constitutes the first experimental demonstration of performance enhancement by recycling photon emission from high-efficiency non-concentrator (one-sun) solar cells. An analysis of the results points to roadmaps for future improvements.

Professor Eli Piasetzky, Department of Physics, Tel-Aviv University
14/10/2013 - 10:30

An ostracon is a piece of pottery or stone that contains writing. We have been studying ostraca written in the ancient Hebrew alphabet from the first Temple era. The writing is in ink on a clay ceramics background, and is sometimes illegible and very difficult to decipher. I will describe our use of modern technologies to document and improve reading of these ancient inscriptions.

      The discipline of palaeography studies the morphology of the letters, their diachronic development over time, and their synchronic variations at a given time. This has been traditionally carried out manually with subjective bias. I will also describe our efforts to introduce the latest developments in image processing and artificial intelligence into this field. Our objective is to date the writing, identify the development of the Hebrew alphabet, find differences between writings from the kingdoms of Israel and Judah, and  to distinguish between different scribes in the individual inscriptions.

Professor Sorin Solomon, Racah Institute, HUJI
17/06/2013 - 10:30

In statistical physics the emergence of large scale collective phenomena out of local interactions between simple agents takes place in general only for very special (zero measure) / critical values of the parameters (temperature, pressure, etc).

Yet in nature collective objects and their large scale dynamics are ubiquitous features dominating our daily experience.
Each of the last decades proposed a different generic mechanism for the emergence of macroscopic complex dynamics out of local microscopic laws.
 
Nowadays it seems that most of the instances in which microscopic events are promoted to macroscopic changes are related to some form of autocatalytic process.
Identifying the relevant autocatalytic process allows one to gain understanding and control on the seemingly messy empirical systems.
 
I will review some of the instances in which the resulting models were analytically tractable and in which the theoretical predictions were confirmed by the data.
Prof. Amnon Aharony, Ben Gurion and Tel Aviv Universities
10/06/2013 - 10:30

Quantum computing requires the ability to write and read quantum information on the spinors of electrons. This work considers mobile electrons, which move through mesoscopic (or molecular) quantum networks (made of quantum wires or of arrays of quantum dots). Combining spin-orbit interactions, whose strength can be tuned by external gate voltages, and the Aharonov-Bohm flux, which can be tuned by an external magnetic field, one can manipulate the properties of such networks, so that the outgoing electrons are polarized along a desired direction. This amounts to 'writing' the desired information on the spinor of the electrons. Given a beam of polarized electrons, the charge conductance of the same network depends on their polarization, allowing 'reading' the qubit information. Specific results will be presented for a simple closed interferometer [1]. The talk will also report on more recent work:

(a) The above filtering is robust against leaking of electrons, in an open interferometer [2]. (b) Filtering can also be achieved for a single one dimensional chain which has spin-orbit interactions, when the chain vibrates in the transverse direction [3].

 

[1] A. Aharony, Y. Tokura, G. Z. Cohen, O. Entin-Wohlman, and S. Katsumoto, Filtering and analyzing mobile qubit information via Rashba-Dresselhaus- Aharonov-Bohm interferometers, Phys. Rev. B 84, 035323 (2011);(arXiv:1103.2232)

[2] S. Matityahu, A. Aharony, O. Entin-Wohlman and S. Katsumoto, Robustness of spin filtering against current leakage in a Rashba-Dresselhaus-Aharonov-Bohm interferometer, Phys. Rev. B 87, 205438 (2013); (arXiv:1302.6772)

 [3] Work with R. I. Shekhter and O. Entin-Wohlman.
Prof. ABRAHAM KATZIR
03/06/2013 - 10:30

There is a wide interest in the development of optical fibers for the mid - IR (i.e. 3-30mm).  AgClBr crystals are extruded in our laboratory to form fibers, which are flexible, non-toxic, non-hygroscopic and highly transparent in the mid-IR.  These silver halide fibers have made it possible to carry out advanced research and development, which will be discussed in this talk:

(1)  Non - contact fiberoptic thermometry.

(2)  Laser power transmission through IR fibers (e.g. laser cutting or heating).

(3)  Laser bonding of tissues - clinical studies.

(4)  Fiberoptic evanescent wave spectroscopy and its applications:

  1. Environmental protection (e.g. monitoring of pollution in water and soil).
  2. Homeland Security (e.g. online monitoring of poisons in water).
  3. Early diagnosis of diseases, such as cancer – clinical studies.

(5)  Periodic structures of IR Fibers:

a.   Thermal imaging through ordered bundles of fibers.

b.   Novel photonic crystal fibers.

(6)   Single mode fibers and waveguides for mid - IR astronomy (e.g. nulling interferometry).

(7)  Doped AgClBr crystals and fibers for mid - IR amplifiers and lasers (e.g. countermeasures against shoulder launched missiles).

(8)  Near-field scanning mid-IR microscopy with a sub-wavelength resolution (e.g. the study of individual living cells or of individual components in integrated electronic circuits).

 

Professor Alexander Grosberg, Center for Soft Matter Physics, New York University
27/05/2013 - 10:30

Each cell of our body contains two meters of DNA stored in ten micrometers nucleus. Why does not it tangle? In the talk, recent numerical, theoretical, and experimental advances in the field will be reviewed in connection to one another. The melt of non-concatenated rings will be presented as a workhorse theoretical model to explain many relevant features, including chromosome territoroes and experimentally observed scaling of contact probabilities.

Prof. Emil Polturak, Faculty of Physics, Technion
20/05/2013 - 10:30

Friction at the macroscopic scale continues to be a thriving research area, in accordance with its undisputed importance in our life. At the microscopic scale, experiments show that in some cases, the friction between two solid surfaces can be vanishingly small. An open problem is whether friction between macroscopic bodies can result from quantum fluctuations. Recent experiments, in which the friction between two slabs of a quantum solid was actually measured, offer a way to answer this question.

Prof. Moshe Gitterman, Dept. of Physics, BIU
13/05/2013 - 10:30

The model of stochastic oscillator subject to additive random force, which includes the Brownian motion, is widely used for analysis of different phenomena in physics, chemistry, biology, economics and social science. As a rule, by the appropriate choice of units one assumed that the particle's mass is equal to unity. However, for the case of an additional multiplicative random force, the situation is more complicate. As we show, for the cases of random frequency or random damping, the mass cannot be excluded from the equations of motion, and, for example, besides the restriction of the size of Brownian particle, some restrictions exist also of its mass. In addition to these two types of multiplicative forces, we consider the random mass, which describes, among others, the Brownian motion with adhesion. The fluctuations of mass are modelled as a dichotomous noise, and the first  two moments of coordinates show non-monotonic dependence on the parameters of oscillator and noise, In the presence of an additional periodic force an oscillator with random mass is characterized by the stochastic resonance phenomenon, when the appearance of noise increases the input signal.

Professor David Biron, Department of Physics, University of Chicago
06/05/2013 - 10:30

All animals sleep, or do they? This question remains controversial. If sleep is truly universal to the animal kingdom then even the simplest model animal, the hydrogen atom of neuroscience if you will, should sleep. The nematode Caenorhabditis elegans develops through four larval stages before it reaches adulthood. At the transition between stages and before it molts, i.e., synthesizes a new exoskeleton and sheds the old one, it exhibits a quiescent state termed lethargus. In a seminal paper in 2008, David Raizen has demonstrated that lethargus bears several similarities to sleep. The talk will describe our contributions to establishing C. elegans lethargus as a model for sleep, as well as related topics. We approach the problem with a combination of behavioral, computational, genetic, physiological and optical techniques. Examples of behavioral dynamics associated with lethargus include the nematode’s hockey stick-like posture and the maneuver that it facilitates, non-Markovian locomotion dynamics (micro-homeostasis) and the modulation of global locomotion states over long timescales. As time permits, the modulation of neuronal activity associated with lethargus, the role of serotonin in sleep-wake transitions, and a novel nematode nociceptor will be briefly discussed.

Gad Koren, Faculty of Physics, Technion
29/04/2013 - 10:30

A simple overview of topological insulators (TI) and topological superconductors (TSC) will be given. TI are bulk insulators with surface conductance. They are robust against disorder and decoherence, and therefore interesting for quantum computing. A TSC can be realized when superconductivity is induced in a TI by the proximity effect with a conventional s-wave superconductor. TSC junctions with a normal metal are predicted to have zero bias conductance peaks in their conductance spectra which originate in Majorana fermions (MF). These MF states might be the basic units of a future quantum computer. Recent experimental results will be presented and discussed in the context of TSC and MF.

Prof. Eran Sharon, The Racah Institute of Physics, HUJI
22/04/2013 - 10:30

 

Many natural structures are made of soft tissue that undergoes complicated shape transformations as a result of the distribution of local active deformation of its "elements". Currently, the ability of mimicking this shaping mode in manmade structures is poor.

I will present some results of our study of actively deforming thin sheets.

We formulated a covariant elastic theory from which we derive an approximate 2D plate/shell theory for sheets with intrinsic incompatible metric and curvature tensors. With this theory we study selected cases of special interest.

Experimentally, we use environmentally responsive gel sheets that adopt prescribed metrics upon induction by environmental conditions. With this system we study the shaping mechanism in different cases of imposed metrics and curvature.

I will focus on different mechanisms that form helical ribbons and will show how the mechanism of seed pod opening is related to shape selection in self assembled chiral macromolecules.

Dr. Beena Kalisky, Department of Physics, Bar-Ilan University
08/04/2013 - 10:30
Complex oxide materials have a broad range of functionality such as ferromagnetism, piezoelectricity, and superconductivity. When combinations of complex oxides are grown as heterostructures, changes in the local electronic-structure at the interface can create new electronic phases that cannot exist in either parent material. One example is the interface formed by growing LAO on STO. Though both materials are insulators, the interface between them shows conductivity, superconductivity and even magnetism.

In the LAO/STO system we discovered nanoscale patches of magnetism coexisting with superconductivity. An outstanding question is what controls the magnetism, and how it relates to the conductivity and superconductivity. I will describe our efforts to answer these questions, by mapping the landscape of ferromagnetism, superconductivity and conductivity with scanning SUQID microscopy. I will focus on our studies of current flow at the interface from a local point of view. We found that at low temperatures the current flows in highly conductive channels that are related to STO tetragonal domain structure. The interplay between substrate domains and the interface provides an additional mechanism for understanding and controlling the behaviors of heterostructures.
Professor Hanoch Gutfreund, Center for Brain Sciences, HUJI
18/03/2013 - 10:30

 

After completing his Special Theory of Relativity, Einstein felt a compelling need to generalize the principle of relativity from inertial to accelerated motion and to include gravitation in the process. He struggled with this task for eight years. At an early stage he was fascinated by the idea that acceleration is equivalent to gravitation, which led him to differential geometry as the basic tool for formulating the new theory. What followed was a series of misinterpretations, wrong paths and simple errors until the "happy end" in November 1915. In 1916, Einstein wrote to Lorentz: "The series of my papers on gravitation is a chain of erroneous paths, which nevertheless gradually brought me closer to my goal."

The lecture will describe this intellectual scientific odyssey.

Dr. Offer Feinerman, Department of Physics, Weizmann Institute
11/03/2013 - 10:30

Biological individuals often interact to form cooperative societies that have functional advantages.
How the specifics of these interactions constrain collective performance is not well
understood. In this context, we study how desert ants inform each other about the presence
of food. We use automated tracking to generate a large data-base of ant trajectories and interactions
that provides us with sufficient statistics to empirically estimate the efficiency of their
communication. This is done, quantitatively, by calculating the information theoretical channel
capacity of the ants' pairwise interactions. We find that this channel is noisy to a degree
that makes it difficult for ants to tell between a recruiter reporting about food and a random
collision within the dark nest environment. To distinguish these ambiguous signals the colony
must therefore perform error-correcting on the level of the group. We demonstrate that the ants
accomplish this by exhibiting strict control of when to transmit a message and when to respond
to received information. This control leads a collective process that couples negative and positive
feedbacks and ensures reliable colony performance. Thus, the ants need no language, but
just one aptly used "word" pronounced with conviction inside a noisy environment.

Professor Adi Nusser, Faculty of Physics, Technion
04/03/2013 - 10:30

The standard cosmological model based on dark energy, standard gravity,
and cold dark matter as the driver for structure formation has passed
important observational tests related to the present distribution of
matter on large scales (larger than a few 10s of Megaparsecs). It will
be argued that deviations from the standard model can be further probed
through signatures of the large scale motions (deviations from pure
Hubble flow) of galaxies. Some constraints on f(R) and DGP gravity will
be described using motions of galaxies in the nearby Universe.
It will be shown how future surveys of ~ a billion galaxies like
Euclid will allow constraints on dark energy models.

Prof. Uri Alon, Physics of Complex Systems, Weizmann Institute
14/01/2013 - 10:30

 

To understand biological systems, our lab has defined "network motifs": basic interaction patterns that recur throughout biological networks, much more often than expected at random. The same small set of network motifs appears to serve as the building blocks of the circuitry that processes information from bacteria to mammals. Specific network motifs may be universal building blocks of biological computation. We experimentally studied the function of each network motif in the bacterium E. coli using dynamic fluorescent measurements from living cells. Each network motif can serve as an elementary circuit with a defined function: filters, pulse generators, response accelerators, temporal-pattern generators and more. Evolution seems to have rediscovered the same motifs again and again, perhaps because they are the simplest and most robust circuits that perform these information-processing functions.
Professor Ulf Leonhardt, Weizmann Institute
07/01/2013 - 10:30

 

Many mass-produced everyday products of modern technology would appear to be completely magical to our ancestors: mobile phones, television, computers, electric light, cars, etc. Some devices that are still perceived as magical or mysterious are about to appear in the laboratory and are not so mysterious after all. For example, the first prototype of an electromagnetic cloaking device has been made at Duke university in 2006. This device makes an object invisible to microwave radiation of a single frequency and polarization. Cloaking devices may also be turned into their exact opposite: perfect lenses that can focus electromagnetic waves with unlimited precision. At Harvard University, first vital steps towards levitating objects on the forces of the quantum vacuum have been made. At St Andrews, we observed first indications of artificial black holes in the laboratory, using extremely short light pulses in photonic-crystal fibres. Invisibility devices, quantum forces and optical black holes have two things in common: they represent applications of Einstein's general relativity in Maxwell's electromagnetism and their practical demonstrations are made possible by modern metamaterials. I will try to elucidate the scientific principles acting behind the scenes of such "pure and applied magic".

Professor Shimon Marom, Department of Physiology and Faculty of Electrical Engineering, Technion
31/12/2012 - 10:30

 

Trial-by-trial response variation is ubiquitous in practically every observable neural scale. I will describe our experimental efforts to measure and interpret these fluctuations over a wide range of timescales in single neurons and large-scale networks, as well as in simple behavioral (psychpohysical) settings. While the statistical nature of the fluctuations is comparable in these different levels of organization, it is difficult - maybe impossible, maybe even meaningless - to attempt accounting for macroscopic fluctuations in terms of microscopic dynamics. Alternative interpretations are offered and experimentally demonstrated.
 
Prof. Kinneret Keren, Dept. of Physics, Technion
24/12/2012 - 10:30 - 12:00

 

Cell movement is driven by a spatially extended, self-organized, mechanochemical machine consisting of numerous actin polymers, accessory proteins and molecular motors. This impressive assembly self-organizes over several orders of magnitude in space and time, from the fast dynamics of individual molecular-sized building blocks to the persistent motion of whole cells over minutes and hours. We focus on the mechanisms underlying this remarkable self-organization using the simplest available model systems. We combine quantitative analysis of cell morphology and spatio-temporal dynamics at the molecular level with biophysical measurements, toward the goal of understanding how global cell shape and movement are determined. Our results feed into and direct the development of quantitative theoretical models of moving cells. 
Dr. Amos Sharoni, Dept. of Physics, Bar-Ilan University
17/12/2012 - 10:30

Spintronics; composed from spins, electrons and electronics; deals with systems which take advantage of both the spin and charge of the electron. Spintronics based devices are promising candidates for novel electronics, but also exhibit intriguing physical phenomena. I will (partially) review advances in this field, and focus on lateral spin valves. These are useful ferromagnetic/non-magnetic devices that can decouple a pure spin current from an electrical current by using a non-local geometry. We have used lateral spin valves to study spin injection, propagation and detection in metallic devices, as function of material choice and geometry.  

Prof. Mordechai Segev, Faculty of Physics, Technion
10/12/2012 - 10:30

Anderson Localization is one of the most basic concepts in solid-state physics.
However, experiments on Anderson localization in electronic systems have eluded
scientists for many decades. Several decades after Anderson's prediction, the
concept has been extended to optics, and in 2007 our group has made the first
demonstration of Anderson localization in its original context, where random
fluctuations superimposed upon a periodic structure bring transport to a halt.
Many experimental works have followed in optics and matter-waves. But can
disorder work to increase transport beyond diffusion, and perhaps even beyond
ballistic transport? The talk will review the recent progress on Anderson
localization of light, and will describe experiments and theory demonstrating
disordered–enhanced transport in photonic quasicrystals, and hyper-transport of
light in photonic media with evolving disorder: a new regime of transport in
which an arbitrary wavepacket expands at a rate faster than ballistic.

Prof. Haim Diamant, School of Chemistry, Tel-Aviv University
03/12/2012 - 10:30

The old field of thin-sheet elasticity, dating back to Euler, has had a
remarkable revival in recent years. One of the main reasons has been the
inadequacy of traditional perturbative approaches to account for patterns
observed in ultra-thin sheets. We will review the recent developments and
then focus on an exemplary problem -- a fluid-supported sheet under
compression -- which exhibits periodic ("wrinkled") and localized
("folded") patterns. This system is integrable and reveals a new and
unexpected symmetry.

Prof. Robijn Bruinsma, Dept. of Physics, UCLA
26/11/2012 - 10:30

Our exquisite sense of hearing has fascinated physicists for more than
a century. It has been well established that hearing is an active, energy consuming,
non-linear process. Major experimental progress over the last decade now allows detailed
comparison between theory and experiment. The talk will review the application of
dynamical systems theory to active hearing as well as experimental tests.

Prof. Yoram Dagan, School of Physics and Astronomy, Tel Aviv University
19/11/2012 - 10:30

Transistors, lasers and solar cells all involve interfacial phenomena. However, while in semiconductors as one moves-away from the interface “free electron” physics takes place, in oxides strong correlations can play an important role. Spin, orbital, and lattice degrees of freedom in the constituting materials can manifest themselves in a new and interesting way at the interface between oxides, bringing new physical concepts and functionalities.   

Since the seminal discovery of Ohtomo and Hwang the interface between SrTiO3 and LaAlO3 became a model system for studying oxide interfaces. Despite the two parent compounds being nonmagnetic insulators a two dimensional electron gas is formed at their interface. This electron gas turned out to be superconducting and magnetic. These properties can be easily tuned using gate voltage that changes the carrier concentration.

In this talk I will review recent developments in oxide interfaces in general and in the LaAlO3/SrTiO3 system in particular. I will describe the physical problems and challenges yet to be surmounted and our group’s effort in this field.

Prof. Fyl Pincus, Departments of Physics and Materials Science, UC Santa Barbara
12/11/2012 - 10:30

Magnetic tweezer studies of the force-elongation of single stranded DNA at various salt concentrations by the Saleh group at UCSB have discovered several distinct scaling regimes.  At relatively high forces, an unusual behavior is observed where L is the end-to-end length and f is the applied force.  I shall review our understanding of these scaling properties with a speculation concerning the logarithmic behavior in analogy to one dimensional ferromagnets.

Professor Nir Davidson, Faculty of Physics, Weizmann Institute
05/11/2012 - 10:30

 

Since the advent of laser cooling in the 80’s ultra cold neutral atoms have been extensively used for precision spectroscopic measurements, mostly under free falling conditions and low atomic density where the perturbations of trapping forces and atomic collisions are minimal. We review recent developments that exploit high density trapped ensembles of ultra cold atoms for precision spectroscopy and quantum memories. We show that the negative role of atomic collisions in limiting the attainable atomic coherence time can be suppressed and sometimes even inverted into a positive role.

Professor David Kessler, Department of Physics, BIU
29/10/2012 - 10:30

 

We discuss the problem of diffusion of cold atoms in an atomic trap. In the semiclassical limit, this problem is equivalent to independent particles undergoing a weakly biased random walk in momentum space. The tails of the momentum distribution are determined by the 1/p fall-off of the bias, and have a power-law decay. This gives rise to anomalous behavior if the exponent of the power-law is sufficiently small in magnitude. Then, the equilibrium prediction is that the average kinetic energy is infinite, which is clearly unphysical. Instead, the system never reaches equilibrium, and the distribution is cut off at momenta of order sqrt(t), rendering all moments finite, but growing in time. We show how a harmonic oscillator with a randomly varying (positive) stiffness gives rise to the same phenomenon. Returning to the atomic trap, we consider the resulting distribution of the atomic positions, which is a cut-off Levy distribution. Finally, we discuss the comparison to experiment.

Prof Eilam Gross,  The Weizmann Institute of Science
22/10/2012 - 10:30 - 12:00

On the 4th of July 2012, both  experiments at the LHC, ATLAS and CMS announced the discovery of a new Higgs like particle.
The story of the Higgs discovery will be told by one of the men inside....

Prof. Allen Goldman, School of Physics and Astronomy, University of Minnesota
21/05/2012 - 10:30

Field effect transistor configurations have been employed as electrostatic alternatives to chemical doping of novel materials. They provide exquisite control of material properties, which may include magnetism and superconductivity.  The technique can be used to tune the superconductor-to–insulator transition.  A recent innovation has been to replace the gate insulator, which is usually a high-dielectric constant material, with an ionic liquid. Ionic liquids are molten salts at room temperature. When used as a gate dielectric, ionic liquids can facilitate extraordinarily large charge transfers because of the formation of an electronic double layer, which is in effect a capacitor with a nanometer scale gap.  Recent work involving ultrathin YBa2Cu3O7−x(YBCO) films gate using electronic double layer transistor configurations involving ionic liquids as gate dielectrics will be discussed.  In essence the entire phase diagram of the compound can be traversed.  In principle electrostatic gating using ionic liquids may provide an alternative approach to searching for new superconductors as it may serve as a means of systematically doping putative parent compounds. 

 

* Supported in part by the NSF under grants NSF/DMR-0709584 and 0854752 and performed in collaboration with Xiang Leng, Javier Garcia-Barriocanal, Joseph Kinney and Boyi Yang.

Prof. Moty Heiblum, Braun Center for Submicron Research, Department of Condensed Matter Physics, Weizmann Institute
14/05/2012 - 10:45

Experiments involving entangling of particles (or systems) may lead either to decoherence, or, alternatively, to coherent interference. I will present three examples of mesoscopic systems, which consist of a two-path electronic Mach-Zehnder interferometer (MZI) coupled to:  (a) 1-d current carrying channel, with shot noise; (b) Fabry-Perot interferometer in a form of a quantum dot (QD); and (c) Another MZI, revealing two-particle interference. In (a), 'post selection' measurement (cross-correlation' of current fluctuations), will recover the lost interference due to the dephasing process.

 

Prof. David Mukamel, Weizmann Institute
07/05/2012 - 10:30

Systems driven out of thermal equilibrium often reach a steady state which under generic conditions exhibits long-range correlations. As a result these systems sometimes share some common features with equilibrium systems with long-range interactions, such as the existence of long range-order and spontaneous symmetry breaking in one dimension, ensemble inequivalence and other properties. Some models of driven systems will be presented, and features resulting from the existence of long-range correlations will be discussed.

Dr. Oleg Gang, Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY 11973, USA
30/04/2012 - 10:30


      The structural plasticity and tunable interactions provided by DNA chains offer a broad range of possibilities to direct the organization of nanoscale objects into well defined systems, as well as to induce the structural transformations on demand. We have studied the assembly of clusters and extended 2D and 3D array architectures from nanoscale components of multiple types driven by DNA recognition and chain effects. Our work explores how DNA-encoded interactions between inorganic nano-components can guide the formation of well-defined superlattices, how the morphology of self-organized structures can be regulated in-situ, and what molecular factors govern a phase behavior. The role of flexible chains, particle anisotropy, and external stimuli on a structure formation and its transformation will be discussed in details. Our recent progress on the assembly of heterogeneous particle superlattices with switchable, tunable, magnetically and optically active properties will be presented.

      Research is supported by the U.S. DOE Office of Science and Office of Basic Energy Sciences under contract No. DE-AC-02-98CH10886.

 

Prof. Larry Horowitz, Bar Ilan University
23/04/2012 - 10:30

The Stueckelberg formulation of a manifestly covariant relativistic classical and quantum

mechanics is briefly reviewed and it is shown that in this framework a simple model

exists for which, for systems with flavor oscillations, measured beam transit times can be

shortened. We show that this phenomenon could provide a mechanism for a “pull back”

in measured time during the transit of a beam of neutrinos but for which the speed is

almost everywhere less than light speed. The model is shown to be consistent with the

field equations and the Lorentz force for Glashow-Salam-Weinberg type non-Abelian fields

interacting with the leptons. This result can be considered as a prediction of the outcome

of experiments designed to resolve the presently conflicting evidence for this effect.

Prof. Ehud Meron, The Physics Department, Ben Gurion University
16/04/2012 - 10:30

The significance of vegetation patchiness to ecosystem function is well recognized. During the past decade an increasing number of studies have appeared, reporting on the observations of self-organized patchiness in a variety of terrestrial and marine ecosystems. In parallel, model studies have uncovered small-scale biomass-resource feedbacks that give rise to periodic and disordered patterns at large scales, and thus explain the observations. However, the implications of vegetation pattern formation for various ecological processes, such as biodiversity change, desertification and rehabilitation have hardly been studied. In this talk I will focus on pattern formation aspects of desertification and rehabilitation. Unlike the common view of desertification as an abrupt transition from a productive stable state to a less productive alternative stable state, pattern formation theory suggests the likelihood of gradual transitions involving extended pauses at many intermediate stable states of decreasing productivity. This finding calls for re-examination of currently proposed warning signals of imminent desertification. Pattern formation theory also suggests a novel view of rehabilitation of degraded landscapes – rehabilitation as a spatial resonance problem. Motivated by this application, we studied the impact of 1d periodic spatial forcing on 2d pattern forming systems, revealing instabilities that shed new light on current rehabilitation practices. I will conclude with a few comments on the significance of integrating pattern formation theory into spatial ecology.

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Prof. Wayne D. Kaplan, Department of Materials Engineering, Technion
02/04/2012 - 10:30

Since the 1980s it has been recognized that the structure of grain boundaries in polycrystalline ceramics can have a diffuse nature, characterized by a ~1nm thick nominally amorphous film.  More recently, the structure of grain boundaries has been described following diffuse interface theory, stating that the structure and chemistry of grain boundaries, interfaces and surfaces can go through two dimensional transitions between thermodynamic states (termed complexions) in order to lower the interface energy.  As such complexions for interfaces are analogous to phases in bulk, although they are not bulk phases.  In the past these conclusions have been reached based on structural characterization of grain boundaries and interfaces correlated with mechanical and electrical properties, and more recently it has been shown that specific complexions can have a significant influence on grain boundary mobility, and thus the morphology of an evolving microstructure.

 

To date, almost all of these studies have been conducted at grain boundaries in single phase polycrystalline systems, which by definition are not at equilibrium, and in some cases it is not even clear if the identified complexions are at steady-state.  Similar questions have been raised for studies focusing on metal-ceramic interfaces from thin film studies, where the deposition process used to form the samples may be very far from equilibrium. 

 

This presentation will focus on an experimental approach to address the structure, chemistry and energy of complexions at metal-ceramic interfaces which are fully equilibrated, from which it can be demonstrated that a change in complexion reduces interface energy.  This will be compared with complexions at solid-liquid interfaces, where a region of ordered liquid exists adjacent to the interface at equilibrium, and the details of a reconstructed solid-solid interface where the reconstructed interface structure accommodates lattice mismatch for a nominally incoherent interface.  These three systems will be compared to known reconstructed solid surfaces, which can also be described as complexions, within a more generalized Gibbs adsorption isotherm.

 

 

 

Prof. Yariv Kafri, Technion
26/03/2012 - 10:30

The talk will consider energy fluctuations of systems in three different settings (i) An isolated systems who's energy is changed by performing non-adiabatic work using a cyclic process (ii) Two systems which are brought in contact and are approaching thermal equilibrium (iii) A driven dissipative system which is driven by non-adiabatic work and coupled to a large bath. Expressions for the size of energy fluctuations as a function of time in all settings will be derived, assuming that the process is composed of many small steps of energy exchange. In all cases the results depend only on average energy flows in the system and densities of states, independent of any other microscopic detail. In the steady-state an expression relating three key properties: the relaxation time of the system, the energy injection rate, and the size of the fluctuations will be presented.

Rof. Guy Ron, Racah Institute of Physics, Hebrew University of Jerusalem
19/03/2012 - 10:30

The radius of the proton, generally assumed to be a well measured and understood quantity has recently come under scrutiny due to highly precise, yet conflicting, experimental results. These new results have generated a host of interpretations, none of which are completely satisfactory. I will present a general overview to the topic, from the early measurements of the 1950s to the high precision experiments performed today. I will further discuss the various radii and measurements and present some of the attempted explanations for the discrepancies observed.

 

 

Prof. Guy Deutscher , Tel Aviv University
12/03/2012 - 10:30

Research on Superconductivity at the nano-scale started well before the term "nano" became fashionable. In early contributions dark field microscopy was used and allowed for the first to measure grain sizes and grain size distributions down to the nano-scale in films of granular Aluminum that comprised many layers of grains. Recently research on granular superconductivity is receiving increased attention because of its enhancement in the vicinity to a metal-insulator transition, predicted high temperature superconductivity in small clusters and a possible competition with magnetism. These new developments will be reviewed.

Prof. Yael Shadmi, The Technion
05/03/2012 - 10:30

Abstract: Supersymmetry is a beautiful theoretical concept. Its possible relation to the electroweak-breaking scale has fascinated physicists for decades: it may stabilize the Higgs mass, and it predicts Dark Matter candidate(s) near this scale. These days, it is being searched for at the Large Hadron Collider (LHC) at CERN. In this colloquium, I will outline the theoretically compelling features of supersymmetry and discuss the current state of LHC searches for it.