Nonreciprocal phonon dichroism induced by Fermi pocket anisotropy in two-dimensional Dirac materials

Electrons in two-dimensional (2D) Dirac materials carry local band geometric quantities, such as the Berry curvature and orbital magnetic moments, which, combined with electron-phonon coupling, may affect the phonon dynamics in an unusual way. Here, we propose intrinsic nonreciprocal linear and circular phonon dichroism in magnetic 2D Dirac materials, which originate from nonlocal band geometric quantities of electrons and reduce to pure Fermi-surface properties for acoustic phonons. We find that to acquire the nonreciprocity, the Fermi pocket anisotropy rather than the chirality of electrons is crucial. Two possible mechanisms of Fermi pocket anisotropy are suggested: (i) trigonal warping and out-of-plane magnetization or (ii) Rashba spin-orbit interaction and in-plane magnetization. As a concrete example, we predict appreciable and tunable nonreciprocal phonon dichroism in 2H-MoTe2 on a EuO substrate. Our finding points to a different route towards electrical control of phonon nonreciprocity for acoustoelectronics applications based on 2D quantum materials.