Phonon Inverse Faraday effect from electron-phonon coupling

TL;DR

This paper develops a microscopic theory for the phonon inverse Faraday effect, explaining how circularly polarized phonons induce magnetization, with estimates aligning with recent experimental observations in SrTiO3.

Contribution

It introduces a general, material-independent formalism based on time-dependent perturbation theory and electron-phonon coupling for the phonon inverse Faraday effect.

Findings

Estimates of magnetic fields in SrTiO3 match experimental data.

The formalism explains angular momentum transfer between ions and electrons.

Potential for phononic control of magnetism is highlighted.

Abstract

The phonon inverse Faraday effect describes the emergence of a DC magnetization due to circularly polarized phonons. In this work we present a microscopic formalism for the phonon inverse Faraday effect. The formalism is based on time-dependent second order perturbation theory and electron phonon coupling. While our final equation is general and material independent, we provide estimates for the effective magnetic field expected for the ferroelectric soft mode in the oxide perovskite SrTiO$_3$. Our estimates are consistent with recent experiments showing a huge magnetization after a coherent excitation of circularly polarized phonons with THz laser light. Hence, the theoretical approach presented here is promising for shedding light into the microscopic mechanism of angular momentum transfer between ionic and electronic angular momentum, which is expected to play a central role in the phononic manipulation of magnetism.