Enhanced Thermal Hall Effect in Nearly Ferroelectric Insulators
Jingyuan Chen, Steven A. Kivelson, Xiao-Qi Sun
Abstract
In the context of recent experimental observations of an unexpectedly large thermal Hall conductivity, ${\ensuremath{\kappa}}_{H}$, in insulating ${\mathrm{La}}_{2}{\mathrm{CuO}}_{4}$ (LCO) and ${\mathrm{SrTiO}}_{3}$ (STO), we theoretically explore conditions under which acoustic phonons can give rise to such a large ${\ensuremath{\kappa}}_{H}$. Both the intrinsic and extrinsic contributions to ${\ensuremath{\kappa}}_{H}$ are large in proportion to the dielectric constant, $\ensuremath{\epsilon}$, and the ``flexoelectric'' coupling, $F$. 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 STO. We predict a larger intrinsic ${\ensuremath{\kappa}}_{H}$ in certain insulating perovskites.