Exploring phonon thermal Hall anisotropies in SrTiO₃

Since the discovery of the phonon thermal Hall effect (THE) a question still remains unsolved: how can phonons support a transverse temperature gradient and acquire handedness in a magnetic field?

Many theories have been proposed since 2019 in between them we find that impurities may influence the scattering of phonons by perturbing the spin environment they are embedded [1]. Other scenarios point out structural transitions that may be playing a role [2]. We explore the existence of any anomalies or crystal domains that may be field-dependent and could influence the local symmetry breaking of phonons and consequently raise a THE.

We performed measurements on several samples of the non-magnetic insulator in SrTiO₃ to check if the transition structure at 105 K, and its change of crystal structure could affect the existence of crystal domains that could explain the nature of the thermal Hall effect. We studied the thermal conductivity and the thermal Hall signal on samples whose edges are parallel to different crystallographic directions. We also applied different cooling processes through the structural transition temperature and measured the transversal gradient in different areas of the samples.