Phonon helicity induced by electronic Berry curvature in Dirac materials

TL;DR

This paper reveals that in two-dimensional Dirac materials, the local electronic Berry curvature can induce a novel phonon angular momentum, termed phonon helicity, which is locked to phonon propagation direction.

Contribution

The study introduces the concept of phonon helicity induced by electronic Berry curvature in Dirac materials, demonstrating a new electron-phonon interaction effect.

Findings

Nonzero local Berry curvature induces phonon angular momentum.

Phonon angular momentum is locked to phonon propagation direction.

Possible experimental detection methods are discussed.

Abstract

In two-dimensional insulators with time-reversal (TR) symmetry, a nonzero local Berry curvature of low-energy massive Dirac fermions can give rise to nontrivial spin and charge responses, even though the integral of the Berry curvature over all occupied states is zero. In this work, we present a new effect induced by the electronic Berry curvature. By studying electron-phonon interactions in BaMnSb$_2$, a prototype two-dimensional Dirac material possessing two TR-related massive Dirac cones, we find that the nonzero local Berry curvature of electrons can induce a phonon angular momentum. The direction of this phonon angular momentum is locked to the phonon propagation direction, and thus we refer it as "phonon helicity", in a way that is reminiscent of electron helicity in spin-orbit-coupled electronic systems. We discuss possible experimental probes of such phonon helicity.