Phonon Thermal Hall Effect in Magnetic Insulators

Phonons are known to generate a thermal Hall effect in various insulators, including multiferroics [1], cuprate Mott insulators [2], and non-magnetic paraelectrics [3], but the underlying mechanism is still unclear. Theoretical proposals for the phonon thermal Hall effect fall into two categories: intrinsic scenarios based on the coupling of phonons to their environment and extrinsic scenarios based on the skew scattering of phonons by disorders like impurities or defects. 

To shed new light on this question, we studied the thermal Hall effect in a simple cubic material, the antiferromagnetic insulator Cu₃TeO₆, which hosts none of the previously encountered special features. Our observation of a large phonon thermal Hall conductivity in Cu₃TeO₆ indicates that the phonon thermal Hall effect is likely to be a fairly common property of solids [4]. To answer the question of what makes phonons chiral in a magnetic field, we studied the thermal Hall effect in Rh-doped Sr₂IrO₄ and observed a 30-fold enhancement of the thermal Hall angle with just 2% of Rh doping [5]. This work provides systematic evidence to support that the scattering of phonons by impurities embedded within a magnetic environment could possibly be the underlying mechanism in the case of antiferromagnetic insulators. 

 

[1] T. Ideue et al., Nat. Mater. 16, 797-802 (2017).

[2] G. Grissonnanche et al., Nature 571, 376 (2019). 

[3] X. Li et al., Phys. Rev. Lett. 124, 105901 (2020).

[4] L. Chen et al., Proc. Natl. Acad. Sci. U.S.A. 119 (34), e2208016119 (2022).

[5] A. Ataei et al., Nat. Phys. (in press), arXiv:2302.03796.