Probing spin-spin correlations and manipulating exchange interactions in the Van der Waals ferromagnet CrSiTe3

Interactions between electrons in solids are responsible for a wide variety of physical phenomena such as magnetism, superconductivity Mott insulators and more. Understanding interactions between electrons, and manipulating them to stabilize desired electronic phases have been the research focus of the strongly correlated electrons community in the past few decades. Ultrafast optics is a unique experimental tool where strong ultrashort pulses of light can be used both to probe a multitude of electronic phenomena, and to excite and manipulate the properties of the electronic system, driving it away from its equilibrium state. In this talk I will show how ultrafast optical techniques can be used to probe spin spin correlations and modify magnetic interactions in a Van der Waals ferromagnet. CrSiTe3 is composed of van der Waals bonded sheets of ferromagnetically interacting Heisenberg spins that, in isolation, would be impeded from long range order by the Mermin-Wagner theorem. I will show that CrSiTe3 evades thislaw via a two-step crossover from two- to three-dimensional magnetic short range order above its Curie temperature (Tc = 31 K), manifested through two previously undetected totally symmetric distortions at T2D ~ 110 K and T3D ~ 60 K serving as a direct probe for measuring intarlayer and interlayer spin-spin correlations. Having understood the interplay between short range correlations and the magnetoelastic distortions I will show how optically induced electron transfer could be used to enhance the magnetic super-exchange interaction and how this manipulation can be detected by optically probing generation of coherent phonons.