Nano Physics
In 1959, before anyone had seen an atom with a microscope, American physicist Richard Feynman predicted the future: the future of nanotechnology. Feynman imagined a world in which man-made variations in the arrangement of atoms would result in fabulous new functionalities, and powerful solutions for pressing problems.
Today, Bar-Ilan University is one of Israel’s most dynamic nanotechnology research centers. The University’s Institute for Nanotechnology and Advanced Materials (BINA) is home to top innovators who publish hundreds of papers a year, collaborate with multi-national corporations and help set the global nano-research agenda.
Bar-Ilan nanoscientists are uncovering fundamental principles that govern the world in which we live, and are creating the technologies of tomorrow.
The Interaction between Spin Polarized Current and Ferromagnetic Domain Walls in SrRuO3
The issue of interaction between current and domain walls is of great importance both for basic research and applications. This is due to the fact that current-induced manipulation of domain walls is one of the most promising routes to control magnetic configurations on the nano scale, which is needed in novel spintronic devices.
Klein's work in this area provides valuable insight to these phenomena in the extremely narrow domain walls found in SrRuO3. Research papers published by his group include a comprehensive study of the effect of domain walls on the electrical current, and a description of the effect of current on domain walls. Their research in this area continues, and currently focuses on magnetic nucleation effects and current-induced magnetic dynamics.
The Planar Hall Effect: Basic Research and Applications
The planar Hall effect (PHE) is the emergence of transverse voltage in a conductor as a function of the magnitude and orientation of in-plane magnetization. Following their discovery of a giant PHE in colossal magneto-resistant manganese-based perovskites (manganites), Klein's group is pursuing two routes.
One route focuses on resolving the intriguing observations that have contributed to the development of transport equations for crystal-symmetry effects. The other route focuses on applying this effect for the development of novel magnetic random access memory and sensitive magnetic sensors. Their current work in this area includes both basic and applied research.
On the basic research level, they are using PHE to elucidate the intriguing interplay between magnetism and electrical transport in manganites of different compositions and dopings. On the applied level, Klein's team is attempting to develop better memory bits and magnetic sensors by fine tuning growth and nano-fabrication, developing analytical models, and using numerical simulations.
Properties of Conducting Interface between SrTiO3 and LaAlO3
Since its recent discovery, the 2-D electron liquid that forms at the interface between the two insulating oxides SrTiO3 and LaAlO3 has attracted considerable interest due to its fascinating properties and its potential key role in future oxide-based electronics and spintronics. Klein’s group has contributed to this discovery by finding evidence for a non-uniform extraordinary Hall effect, which indicates non-uniform field-induced magnetization.
In addition, they have contributed to elucidating the angular dependence of the magneto-resistance in this system. Current efforts focus on studying the interplay between transport and magnetism in this system.
Materials Science: Soft Matter Physics
Our team works to develop analytical theories and mathematical models of gels, i.e., networks of polymer chains permeated by solvents.
In addition, we develop computer simulations of idealized polymer networks to better understand phase transitions in such systems, such as microphase separation inside gels and the way the structural inhomogeneity of these networks affects both their macroscopic elasticity and their microscopic characteristics as manifested in neutron, x-ray and light scattering studies.
Bio-Nanotechnology
By examining the forces at work when DNA and proteins penetrate membranes, we are assisting with the development of a new approach to sequencing individual strands of DNA, based on tracking their electric field induced passage through nanopores in biological and artificial holes membranes.
By examining the forces at work when DNA and proteins penetrate membranes, we are assisting with the development of a new approach to sequencing individual strands of DNA, based on tracking their electric field induced passage through nanopores in biological and artificial holes membranes.
In a related project, our team studies transport through nuclear pores, which act as “gates” that selectively allow the passage of mRNA and of proteins from the nucleus to the cytoplasm and back. We develop computer simulations of the proteins (nucleoporins) that form the “hairy” pores and determine their permeability and selectivity.
DNA Assemblies
When DNA molecules are grafted to a surface, the result is a densely packed DNA monolayer with unique properties. These stretched DNA molecules can be used as a probe for detecting various proteins and other complementary single-stranded DNA molecules.
In collaboration with experimentalists, we attempt to understand the physio-chemical properties of these monolayers.
Our team is also investigating whether DNA which forms binary complexes (the celebrated double helix) in solution, can exhibit alternate modes of organization in such monolayers.
DNA Topology and Elasticity and DNA-Protein Interactions
We study DNA topology, with a particular focus on how DNA molecules can be closed to form “knots.” We study the probability of the formation of knots of different complexities, how the presence of such knots affects thermal fluctuations, and how to pack DNA in such a way to avoid knotting (such knot-free state of chromatin has been predicted by our team andProf. Alexander Grosberg of New York University, and was recently observed by several molecular cell biology teams).
We develop mathematical models and computer simulations to describe and simulate such knots both in the absence and in the presence of topoisomerases, i.e., enzymes that facilitate the “cutting and pasting” of DNA and thereby allow for its disentanglement.
Our group also studies DNA-protein interactions with emphasis on DNA bending proteins, in order to understand both how the binding of such proteins is affected by the elasticity and the topology of DNA, and the effect of such binding on its elastic and topological properties.
Photonics and Optics Research
In collaboration with industrial partners, Rosenbluh has developed a laser-based atomic clock that is ten times smaller than those currently available and requires a hundred times less power to operate. To improve clock accuracy, his team is working on an atomic beam based compact atomic clock.
Rosenbluh has also used nanofabrication techniques for making plasmonic nano-arrays, which have been shown to highly enhance surface Raman scattering. Such surface arrays may lead to the creation of more powerful tools for the identification of rare molecules.
In other applications of plasmonic structures, a novel detector based on a nano-well filled with semiconductor quantum dots and surrounded by a plasmonic lens focusing element has been demonstrated.
In the application of nanofabrication to optical waveguide structures in silicon, Rosenbluh, in collaboration with Prof. Valentine Freilikher of the Department of Physics, has been working on introducing random nanostructures into the waveguide which can be used to optically switch or modulate the waveguide transmission at extremely high speeds.
The scattering of coherent light by the nanostructures is also of great interest in fundamental studies of light localization in scattering media.
Rosenbluh and his team are also developing in fiber saturable absorbers, based on single walled carbon nanotubes, which can be used to mode-lock fiber lasers. The insertion of the carbon nanotubes in a fixed orientation is also expected to lead to controllable polarization properties. These can be useful in fiber polarization control of fiber lasers.
Communications and Security Research
The generation of random bit sequences based on non-deterministic physical mechanisms is of paramount importance for cryptography and secure communications. High data rates require extremely fast generation rates which are the currently available technology cannot provide.
To resolve these problems, Rosenbluh, in conjunction with Prof. Ido Kanter, has developed an ultrafast random bit generator, based on a chaotic semiconductor laser, with time-delayed self-feedback. The generator, which holds the world record for generation rate, has additional interesting properties which can be applied to cryptography and secure optical communications amongst multiple users and networks.
Superconducting Nanowires and Loops
Recently, Yeshurun’s group, in collaboration with a group at Brookhaven National Laboratories in New York, fabricated thin films patterned with large arrays of superconducting nanowires and loops. These arrays are able to carry electric current with no resistance when cooled below approximately 30 degrees kelvin (-243 degrees Celsius).
Even more interestingly, the material's electrical resistance can be changed in an unexpected way when exposed to an external magnetic field. Such superconducting nanowires and nano-loops may eventually be useful for new electronic devices.
Renewable Energy: Protection from Power Faults Using Superconductors
In 2010, a “fault current limiter” device developed by Yeshurun in conjunction with Dr. Shuki Wolfus and Dr. Alex Friedman was named one of the top five technological breakthroughs by General Electric Corporation. This passive auto-triggering system – which protects the electrical distribution and transmission grids from faulty currents – is being commercially developed by an Israeli startup company called GridON Ltd., and has already won the ACES Award for academic inventors.
Nanotechnology
Sharoni and his team study the physical properties of devices and materials on the nanoscale. They aim to understand how the properties of matter change when the characteristic length scale and dimensionality of a system is drastically altered.
In Sharoni’s lab, research focuses on phase transitions at the nanoscale and on spintronics, an area of study that involves the manipulation of both the intrinsic spin of the electron and its electronic degrees of freedom in solid-state devices.
Phase Transitions
In Sharoni’s lab, the group investigates how the properties of phase transition in condensed matter change with the dimensionality and size of the system under investigation. When the size of the system is shorter (in one or more dimensions) than an important length scale (e.g. the mean free path), the physical properties associated with this length scale are also expected to change.
In Sharoni’s lab, the group investigates how the properties of phase transition in condensed matter change with the dimensionality and size of the system under investigation. When the size of the system is shorter (in one or more dimensions) than an important length scale (e.g. the mean free path), the physical properties associated with this length scale are also expected to change.
In addition, at short length scales, when one material is in close proximity to another material that has different properties, the first material’s properties are affected.
Sharoni and his group have identified avalanche-like transitions of the phase transition in vanadium oxide when measuring nano-size devices of this material. A statistical power-law dependence of the avalanche magnitude points toward the criticality of the transition.
Spintronics
All electronic gadgets rely on the electron, the basic unit of charge, to perform computations and provide power for operations.
In addition to the charge, the electron carries another property called “spin,” a small magnetic field that can be “spun” up or down. Sharoni and his group work to better understand how to measure and manipulate spin properties.
Their research may yield promising technical applications, as one major factor that slows down today’s computers is that their memory and processor computing elements are separate. Spintronics enables the combination of computation and memory into one device, and can theoretically enable computers to operate with less power and at a faster speed.
In addition, spintronics research has facilitated the observation of many new basic physical phenomena. By constructing nano-size devices of hybrid magnetic/non-magnetic origin, Sharoni and his team tap into the spin properties before these effects average out (on a longer length scale).
They have recently measured the effect of copper channel thickness on spin diffusion length and on spin injection efficiency. By modeling the spin injection to a diffusion model, they found an enhanced spin scattering from the ferromagnetic/non-magnetic interface.
Crystal Nucleation in Colloidal Spheres
Sloutskin and his team employ confocal microscopy and light scattering to study crystal nucleation in systems of colloids , which are micron-sized particles undergoing Brownian motion in a liquid.
Crystal nucleation is common, yet still poorly understood; theoretical crystallization rates usually miss the experimental values by many orders of magnitude. While colloids form crystals, mimicking atoms and molecules, they are sufficiently large such that the formation of crystalline nuclei is directly observable via sub-particle resolution confocal microscopy.
Sloutskin’s group, in collaboration with the research team of Prof. David Weitz at Harvard, perform three dimensional, real-time tracking of ~5e4 individual particles in a macroscopic colloidal suspension. They detect the formation of the crystalline nuclei, and measure their morphology and size distribution.
The information obtained, which is not available via any other experimental technique, provides a basis for testing the fundamental assumptions of the theories of crystal nucleation. In contrast with the assumptions of classical nucleation theory, crystalline nuclei are non-spherical.
Moreover, instead of being compact, the nuclei adopt a wide range of more ramified shapes. The large variety of shapes accessible to these nuclei entropically stabilizes them, increasing the rate of nucleation by many orders of magnitude.
Spherically Anisotropic Colloids
Most molecules in nature are spherically anisotropic, which gives rise to unique types of collective behavior both in bulk material and within various interfacial phases.
In bulk phases, the anisotropy may give rise to liquid crystalline phases; at the interfaces, the anisotropy may be responsible for the formation of quasi-two-dimensional surface-frozen phases. While the formation of liquid-crystalline phases and surface freezing transitions have been intensively studied during the last decades, conventional techniques do not allow imaging of individual particles in real-time.
Thus, the physical mechanisms driving these phase transitions have remained obscure.Sloutskin’s group employs colloidal spheroids (ellipsoids of revolution) to mimic the behavior of spherically anisotropic atoms and molecules, hoping to shed light on the physics of liquid crystalline phase formation, as well as surface freezing phenomena.
Structure of Non-Crystalline Sediments
One of the most fundamental, yet poorly understood topics in condensed matter physics is the formation of glass and random close-packed materials, which possess the mechanical properties of solids in the absence of long-range crystalline symmetry.
During centrifugation, colloidal particles, density mismatched with their solvent, form a randomly close-packed sediment.
Sloutskin’s team studies colloidal sediments using a combination of analytical centrifugation techniques and confocal microscopy, searching for the fingerprints of a hidden order parameter, which may play an important role in these seemingly random phases of matter.
