Phonon angular momentum induced by Terahertz electric field

TL;DR

This paper theoretically demonstrates how terahertz electric fields can induce and control phonon angular momentum in polarized materials, revealing resonance effects and potential for experimental measurement.

Contribution

It introduces a novel method to generate and regulate phonon angular momentum using terahertz electric fields, expanding possibilities beyond previously limited materials.

Findings

Large phonon AM generated at phonon resonance frequencies

Resonance observed in the imaginary part of response coefficient

Oscillation of phonon AM measurable via orbital magnetization

Abstract

Despite the growing interest in phonon angular momentum (AM) in recent years, current studies remain limited to a few materials due to the constraints imposed by time reversal symmetry on macroscopic phonon AM. In this work, we theoretically investigate the generation of total phonon AM through alternating terahertz electric fields in polarized materials. In contrast to previous studies on phonon AM, here the off-diagonal elements of the phonon AM operator play an essential role. According to our formula, the large AM is generated when the energy of incident electric fields matches the frequency of optical phonons at {\Gamma} point. Furthermore, a specific resonance on the imaginary part of the response coefficient, as well as periodic regulation of the phonon AM by the phase difference of the driving field, is observed. In polar material GaN, the oscillation maximum is observed as \hbar per unit cell which can be experimentally measured through orbital magnetization induced by phonon AM. Our work offers a promising approach to generate observable phonon AM in a wider range of materials, advancing both the understanding of phonon fundamental physics and potential applications in phononic devices.