Abstract: As a thermal analog of the electrical Hall effect, the thermal Hall effect has emerged as a powerful probe in detecting charge-neutral excitations in insulating materials. Phonons, unlike magnons, were long believed to be incapable of generating a thermal Hall effect due to the lack of charge and spin. However, over the past decades, a sizable phonon thermal Hall effect has been observed in various insulators, including multiferroics [1], cuprate Mott insulators [2], and non-magnetic paraelectrics [3]. Despite these experimental advances, the underlying mechanism is still unclear. Existing theoretical proposals broadly 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.

In this talk, I will first introduce the experimental techniques and possible mechanisms for phonon-mediated thermal Hall effect. I will then present our work on the conventional phonon thermal Hall effect in a simple antiferromagnet insulator Cu3TeO6 [4]. Building on this, I will introduce our discovery of a phonon thermal Hall effect in a more exotic configuration, namely a “planar” configuration where the magnetic field is in parallel to the heat current, in a Kitaev candidate material Na2Co2TeO6 [5] and in cuprates [6]. These results reveal another facet of the still puzzling phonon thermal Hall effect, i.e. it also occurs in a “planar” configuration. Our observations indicate that the phonon thermal Hall effect is likely to be a fairly common property of solids.

[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] Chen, L. et al. Planar thermal Hall effect from phonons in a Kitaev candidate material, Nat. Commun. 15, 3513 (2024).
[6] Chen, L. et al. Planar thermal Hall effect from phonons in cuprates, Phys. Rev. X 14, 041011 (2024).

Speaker bio: Dr. Chen joined the Department of Physics at the University of Illinois Urbana-Champaign as an Assistant Professor as recently as January 2026. Before this, Dr. Chen received her B.S. from the School of Physics at Peking University in 2014 and her Ph.D. in Physics from University of Michigan Ann Arbor in 2020. She was a Prize Postdoctoral Fellow at Université de Sherbrooke in the Prof. Louis Taillefer's lab, and subsequently a Postdoctoral Fellow at University of California Berkeley.