Phonon thermal Hall effect in strontium titanate

Abstract

It has been known for more than a decade that phonons can produce an off-diagonal thermal conductivity in presence of magnetic field. Recent studies of thermal Hall conductivity, ${\kappa }_{xy}$, in a variety of contexts, however, have assumed a negligibly small phonon contribution. We present a study of ${\kappa }_{xy}$ in quantum paraelectric SrTiO${}_3$, which is a non-magnetic 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, ${\kappa }_{xy}(T)$ and $\kappa (T)$ peak at the same temperature and the former decreases faster than the latter at both sides of the peak. Interestingly, in the case of La${}_2$CuO${}_4$ and $\alpha$-RuCl${}_3$, ${\kappa }_{xy}(T)$ and $\kappa (T)$ peak also at the same temperature. We also studied KTaO${}_3$ and found a small signal, indicating that a sizable ${\kappa }_{xy}(T)$ is not a generic feature of quantum paraelectrics. Combined to other observations, this points to a crucial role played by antiferrodistortive domains in generating ${\kappa }_{xy}$ of this solid.

Main text: 6 pages, 4 figures, Supplemental Material is included. Accepted by Phys. Rev. Lett