Phonon Thermal Hall Effect in Strontium Titanate
Xiaokang Li, Benoît Fauqué, Zengwei Zhu, Kamran Behnia
Abstract
It has been known for more than a decade that phonons can produce an off-diagonal thermal conductivity in the presence of a magnetic field. Recent studies of thermal Hall conductivity, ${\ensuremath{\kappa}}_{xy}$, in a variety of contexts, however, have assumed a negligibly small phonon contribution. We present a study of ${\ensuremath{\kappa}}_{xy}$ in quantum paraelectric ${\mathrm{SrTiO}}_{3}$, which is a nonmagnetic insulator and find that its peak value exceeds what has been reported in any other insulator, including those in which the signal has been qualified as ``giant.'' Remarkably, ${\ensuremath{\kappa}}_{xy}(T)$ and $\ensuremath{\kappa}(T)$ peak at the same temperature and the former decreases faster than the latter at both sides of the peak. Interestingly, in the case of ${\mathrm{La}}_{2}{\mathrm{CuO}}_{4}$ and $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{RuCl}}_{3}$, ${\ensuremath{\kappa}}_{xy}(T)$ and $\ensuremath{\kappa}(T)$ peak also at the same temperature. We also studied ${\mathrm{KTaO}}_{3}$ and found a small signal, indicating that a sizable ${\ensuremath{\kappa}}_{xy}(T)$ is not a generic feature of quantum paraelectrics. Combined to other observations, this points to a crucial role played by antiferrodistortive domains in generating ${\ensuremath{\kappa}}_{xy}$ of this solid.