Light Driven Spontaneous Phonon Chirality and Magnetization in Paramagnets

TL;DR

This paper demonstrates how linearly polarized light can induce spontaneous symmetry breaking in paramagnets, leading to chiral phonons and magnetization through nonlinear spin-phonon coupling.

Contribution

It reveals the inherent nonlinearity in spin-phonon coupling and predicts spontaneous symmetry breaking driven by light in paramagnetic materials.

Findings

Spontaneous symmetry breaking occurs under periodic light drive.

Emergence of coherent chiral phonons and magnetization.

Analytical model predicts parameter regimes for symmetry breaking.

Abstract

Spin-phonon coupling enables the mutual manipulation of phonon and spin degrees of freedom in solids. In this study, we reveal the inherent nonlinearity within this coupling. Using a paramagnet as an illustration, we demonstrate the nonlinearity by unveiling spontaneous symmetry breaking under a periodic drive. The drive originates from linearly polarized light, respecting a mirror reflection symmetry of the system. However, this symmetry is spontaneously broken in the steady state, manifested in the emergence of coherent chiral phonons accompanied by a nonzero magnetization. We establish an analytical self-consistent equation to find the parameter regime where spontaneous symmetry breaking occurs. Furthermore, we estimate realistic parameters and discuss potential materials that could exhibit this behavior. Our findings shed light on the exploration of nonlinear phenomena in magnetic materials and present possibilities for on-demand control of magnetization.