Phonon helicity induced by electronic Berry curvature in Dirac materials

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 BaMnSb2, 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.

Probing Nieh-Yan anomaly through phonon dynamics in the Kramers-Weyl semimetals of chiral crystals

“…1b), analogous to the helical spin texture in spin-orbit coupled electronic band structures. Thus, we term it as "phonon helicity" 59 . The phonon helicity can be probed through measuring the total PAM induced by a temperature gradient 60 .…”