Dynamical Multiferroicity

TL;DR

This paper introduces a formalism for dynamical multiferroicity, showing how time-dependent electric polarization can induce magnetization, with applications to phonon-driven effects and magnon excitation in materials.

Contribution

It develops a theoretical framework for dynamical multiferroic effects driven by optical phonons and explains recent experimental observations using this formalism.

Findings

Computed phonon Zeeman effect strength using density functional theory.

Described resonant magnon excitation by optically driven phonons.

Interpreted electromagnons and inverse Faraday effect via dynamical multiferroicity.

Abstract

An appealing mechanism for inducing multiferroicity in materials is the generation of electric polarization by a spatially varying magnetization that is coupled to the lattice through the spin-orbit interaction. Here we describe the reciprocal effect, in which a time-dependent electric polarization induces magnetization even in materials with no existing spin structure. We develop a formalism for this dynamical multiferroic effect in the case for which the polarization derives from optical phonons, and compute the strength of the phonon Zeeman effect, which is the solid-state equivalent of the well-established vibrational Zeeman effect in molecules, using density functional theory. We further show that a recently observed behavior -- the resonant excitation of a magnon by optically driven phonons -- is described by the formalism. Finally, we discuss examples of scenarios that are not driven by lattice dynamics and interpret the excitation of Dzyaloshinskii-Moriya-type electromagnons and the inverse Faraday effect from the viewpoint of dynamical multiferroicity.