Dynamical Orbital Angular Momentum Induced by Circularly Polarized Phonons

TL;DR

This paper demonstrates that circularly polarized phonons can dynamically induce orbital angular momentum in electrons through Berry phase effects, providing a new mechanism for orbitronics in materials with weak spin-orbit coupling.

Contribution

It introduces a microscopic and effective model linking phonon chirality to electron orbital angular momentum, applicable to various materials including transition metal dichalcogenides.

Findings

Circularly polarized phonons induce electron OAM via Berry phase.

The sign of induced OAM depends on phonon chirality.

The mechanism applies to materials with weak spin-orbit coupling.

Abstract

We show that the orbital angular momentum (OAM) of electrons is dynamically induced by circularly polarized phonons. The induced OAM originates from the adiabatic evolution in which electrons acquire Berry phase formulated in terms of the Berry curvature encoded in phonon displacement space. By introducing a tight-binding model with $p$ orbitals on a honeycomb lattice, we show a microscopic picture that ionic rotations modulate orbital overlaps of electrons, and calculate the generated OAM, whose sign depends on phonon chirality. We then construct an effective model for valley phonons with different phonon pseudoangular momenta (PAM) and identity their distinct intervalley-scattering channels. Our model obeys the selection rule between phonons and electrons with the orbital degree of freedom. Extending this framework to $d$-orbital electrons, our model is applied to describe the induced OAM in monolayer transition metal dichalcogenides. Our results reveal a direct orbital generation mechanism that emerges even in materials with weak spin-orbital coupling, opening a new promising way for orbitronics applications.