Thermal Hall Resistivity as a Unifying Description of Phonon Thermal Hall Effect in Various Insulators
A considerable phonon thermal Hall effect was recently discovered across a diverse collection of materials. To clarify this enigmatic thermal Hall response in various insulators, we investigate the doped Mott insulator La$_{5/3}$Sr$_{1/3}$NiO$_4$ as an example material system and reveal a characteristic phonon-dominated thermal Hall effect. As a sensitive probe of the transverse thermal response, the thermal Hall resistivity $w_{xy}$ exhibits an insulating-like temperature dependence $w_{xy}(T)$, a linear magnetic-field dependence $w_{xy}(H)$ near $H=0$, and a $T$-linear thermal Hall angle at low temperatures. The presence of similar phenomena across a series of insulators suggests that $w_{xy}$ serves as a unifying description of phonon thermal Hall effect, corroborated by an apparent correlation between the insulating-like $w_{xy}(T)$ and material's localized electronic state.