Seminars
Speaker: 齊藤 巧真 (東京大学)
Date & Time: 2020年2月14日午前10:30-11:30
Room: 本郷キャンパス工学部6号館3階セミナー室B
Title: Theory of phonon Hall effect in nonmagnetic insulators
Abstract:
Recently, thermal transport physics is acquiring more and more interest. In particular, thermal Hall conductivity of insulators manifests the topological nature of band structures of bosonic quasiparticles such as phonons and magnons [1,2]. The origins of nonzero Berry curvature of phonons and magnons are highly nontrivial since they have no electric charge and hence do not undergo the Lorentz force. As for phonons, Hall effect of them is only observed in magnetic materials [3], and all existing theories assume the spin-phonon interaction [4].
In a sharp contrast, we theoretically propose a new mechanism of phonon Hall effect in nonmagnetic insulators by investigating lattice dynamics under magnetic field beyond the Born-Oppenheimer (BO) approximation. Correction term to the conventional BO approximation is given by the Berry curvature in the nuclear coordinate space [5], which leads to direct coupling of phonons and magnetic field. We assume a simplified model for the nonmagnetic band insulator, and calculate the Berry curvature and thermal Hall conductivity induced by it. We find that the Berry curvature is determined by overlap integrals between neighboring atomic orbitals [6].
[1] T. Qin, et al., Phys. Rev. B 86, 104305 (2012)
[2] R. Shindou, et al., Phys. Rev. B 87, 174427 (2013)
[3] C. Strohm, et al., Phys. Rev. Lett. 95, 155901 (2005)
[4] L. Sheng, et al., Phys. Rev. Lett. 96, 155901 (2006)
[5] A. Mead, Rev. Mod. Phys. 64, 51 (1992)