Talks and presentations

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High Resolution Polar Kerr Effect Studies of CsV3Sb5

March 08, 2023

Talk, Caesars Forum, Las Vegas, Nevada

We report high resolution polar Kerr effect measurements on CsV3Sb5 single crystals in search for signatures of spontaneous time reversal symmetry breaking below the charge order transition at T* = 94 K. Utilizing two different versions of zero-area loop Sagnac interferometers operating at 1550 nm wavelength, each with the fundamental attribute that without a time reversal symmetry breaking sample at its path, the interferometer is perfectly reciprocal, we find no observable Kerr effect to within the noise floor limit of the apparatus at 30 nanoradians. Simultaneous coherent reflection ratio measurements confirm the sharpness of the charge order transition in the same optical volume as the Kerr measurements. At finite magnetic field we observe a sharp onset of a diamagnetic shift in the Kerr signal at T*, which persists down to the lowest temperature without change in trend. Since 1550 nm is an energy that was shown to capture all features of the optical properties of the material that interact with the charge order transition, we are led to conclude that it is highly unlikely that time reversal symmetry is broken in the charge ordered state in CsV3Sb5.

Anomalous elasticity of 2D materials beyond self–consistent approximation

March 03, 2020

Talk, Colorado Convention Center, Denver, Colorado

We study elastic properties of two–dimensional crystalline materials, such as graphene. It is known that in 2D membranes strong thermal fluctuations of flexural phonons lead to dramatic change of phonon spectrum and, as a result, in anomalous material–independent elastic properties, such as non-linear Hooke’s law under the low stress and auxetic behavior. We compute elastic moduli η and Poisson ratio ν of 2D membrane in the approximation of high embedded dimensionality. We go beyond one-loop approximation and find that famous self-consistent screening approximation is only as good as first-order approximation. Most remarkably, we analyze a case of disordered membrane and find new disorder–dominant phase, where all the critical exponents are different from the clean case. We find that phase transition happens at finite temperature in contrast to the prediction given by self–consistent screening approximation, that transition is only possible at absolute zero.

Landau levels and magnetic tunneling in Weyl semimetals and magnetoconductance of ballistic junctions

May 25, 2018

Talk, Landau Institute of Theoretical Physics, Moscow, Russia

We study the Landau levels of a Weyl semimetal with two adjacent Weyl nodes. We consider different orientations of magnetic field with respect to the vector of Weyl node splitting. A magnetic field facilitates the tunneling between the nodes, giving rise to a gap in the transverse energy of the zeroth Landau level. We show how the spectrum is rearranged at different orientations and how this manifests itself in the change of behavior of the differential magnetoconductance of a ballistic p-n junction.