Enhanced Thermal Hall Effect in Nearly Ferroelectric Insulators

Abstract: Thermal Hall measurement has become increasingly important in condensed matter physics. In the context of recent experimental observations of an unexpectedly large thermal Hall conductivity in insulating La2CuO4 and SrTiO3, collaborators and I theoretically explore conditions under which acoustic phonons can give rise to such a large thermal Hall effect. Both the intrinsic and extrinsic contributions to the thermal Hall conductivity are large in proportion to the dielectric constant and the flexoelectric coupling. While the intrinsic contribution is still orders of magnitude smaller than the observed effect, an extrinsic contribution proportional to the phonon mean free path appears likely to account for the observations, at least in SrTiO3. We predict a larger intrinsic and/or extrinsic contribution to thermal Hall effect in certain insulating perovskites. I will discuss the implications for existing and future thermal Hall experiments, as well as new theoretical problems to explore.

Reference: [1910.00018], with Steven Kivelson and Xiao-Qi Sun