Léo Mangeolle (TUM, Munich)

Thermal Hall conductivity of neutral bosons from the quantum kinetic equation

Thermal Hall conductivity has recently emerged as an experimentally accessible property of insulating materials. Theoretical understanding thereof has remained a challenge, in particular since the breaking of time-reversal symmetry by neutral particles is nontrivial and can emerge from multiple mechanisms (semiclassical dynamics, skew-scattering, etc). In a first part, I will present a general formulation of inelastic skew-scattering of energy-carrying bosons by other collective excitations. Specializing to phonon-magnon interactions, I will show that a phonon thermal Hall effect from skew-scattering in antiferromagnets is allowed by magnetoelastic and spin-orbit couplings. In a second part, I will focus on the free semiclassical dynamics of neutral bosons, and present a systematic derivation of their kinetic equation, incorporating the topological dynamics of wavepackets in the form of Berry curvatures (generalized to phase space). This makes it possible to treat inhomogeneous systems, including boundaries, textures, etc., in a compact and natural manner.