All Publications

  • High Resolution Polar Kerr Effect Studies of CsV_{3}Sb_{5}: Tests for Time-Reversal Symmetry Breaking below the Charge-Order Transition. Physical review letters Saykin, D. R., Farhang, C., Kountz, E. D., Chen, D., Ortiz, B. R., Shekhar, C., Felser, C., Wilson, S. D., Thomale, R., Xia, J., Kapitulnik, A. 2023; 131 (1): 016901


    We report high resolution polar Kerr effect measurements on CsV_{3}Sb_{5} single crystals in search of 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 CsV_{3}Sb_{5}.

    View details for DOI 10.1103/PhysRevLett.131.016901

    View details for PubMedID 37478434

  • Anomalous thermal transport and strong violation of Wiedemann-Franz law in the critical regime of a charge density wave transition PHYSICAL REVIEW B Kountz, E. D., Zhang, J., Straquadine, J. W., Singh, A. G., Bachmann, M. D., Fisher, I. R., Kivelson, S. A., Kapitulnik, A. 2021; 104 (24)
  • Sample shape and boundary dependence of measured transverse thermal properties JOURNAL OF APPLIED PHYSICS Mumford, S., Paul, T., Kountz, E., Kapitulnik, A. 2020; 128 (17)

    View details for DOI 10.1063/5.0024253

    View details for Web of Science ID 000589711700001

  • Thermal diffusivity above the Mott-Ioffe-Regel limit PHYSICAL REVIEW B Zhang, J., Kountz, E. D., Levenson-Falk, E. M., Song, D., Greene, R. L., Kapitulnik, A. 2019; 100 (24)
  • Thermalization and possible signatures of quantum chaos in complex crystalline materials. Proceedings of the National Academy of Sciences of the United States of America Zhang, J., Kountz, E. D., Behnia, K., Kapitulnik, A. 2019


    Analyses of thermal diffusivity data on complex insulators and on strongly correlated electron systems hosted in similar complex crystal structures suggest that quantum chaos is a good description for thermalization processes in these systems, particularly in the high-temperature regime where the many phonon bands and their interactions dominate the thermal transport. Here we observe that for these systems diffusive thermal transport is controlled by a universal Planckian timescale [Formula: see text] and a unique velocity [Formula: see text] Specifically, [Formula: see text] for complex insulators, and [Formula: see text] in the presence of strongly correlated itinerant electrons ([Formula: see text] and [Formula: see text] are the phonon and electron velocities, respectively). For the complex correlated electron systems we further show that charge diffusivity, while also reaching the Planckian relaxation bound, is largely dominated by the Fermi velocity of the electrons, hence suggesting that it is only the thermal (energy) diffusivity that describes chaos diffusivity.

    View details for DOI 10.1073/pnas.1910131116

    View details for PubMedID 31515452