Anomalous circular phonon dichroism in transition metal dichalcogenides

TL;DR

This paper reveals that transition metal dichalcogenides exhibit magnetization-induced circular phonon dichroism driven by pseudogauge electron-phonon coupling, enabling tunable acoustic phonon absorption without Landau levels.

Contribution

It uncovers a novel mechanism for phonon dichroism in 2D materials involving pseudogauge coupling, independent of Landau levels, with potential for tunable acoustoelectronic applications.

Findings

Large dichroism signal in monolayer MoTe2 on EuO substrate.

Reciprocal and nonreciprocal absorption of circular phonons upon reversing propagation and magnetization.

Gate voltage enables tunable circular phonon dichroism.

Abstract

A magnetic field can generally induce circular phonon dichroism based on the formation of Landau levels of electrons. Here, we study the magnetization-induced circular phonon dichroism in transition metal dichalcogenides, without forming Landau levels. We find that, instead of the conventional deformation potential coupling, pseudogauge-type electron-phonon coupling plays an essential role in the emergence of the phenomenon. As a concrete example, a large dichroism signal is obtained in monolayer MoTe2 on a EuO substrate, even without considering Rashba spin-orbit coupling. Due to the two-dimensional spin-valley-coupled band structure, MoTe2 shows a reciprocal and nonreciprocal absorption of circularly polarized acoustic phonons upon reversing the direction of phonon propagation and magnetization, respectively. By varying the gate voltage, a tunable circular phonon dichroism can be realized, which paves a way toward different physics and applications of two-dimensional acoustoelectronics.