Magnetization and phase transition induced by circularly polarized laser in quantum magnets

TL;DR

This paper predicts a laser-induced nonequilibrium phase transition in quantum spin systems, where circularly polarized light can coherently control magnetization and induce ultrafast magnetic state changes.

Contribution

It introduces a theoretical framework for laser-induced magnetization and phase transitions in quantum magnets, supported by numerical simulations and physical mechanism elucidation.

Findings

Numerical demonstration of magnetization perpendicular to laser polarization in an S=1 antiferromagnetic chain.

Identification of a new magnetic state replacing the Haldane phase under laser influence.

Theoretical prediction applicable to general quantum spin systems with magnetic anisotropy.

Abstract

We theoretically predict a nonequilibrium phase transition in quantum spin systems induced by a laser, which provides a purely quantum-mechanical way of coherently controlling magnetization. Namely, when a circularly polarized laser is applied to a spin system, the magnetic component of a laser is shown to induce a magnetization normal to the plane of polarization, leading to an ultrafast phase transition. We first demonstrate this phenomenon numerically for an $S=1$ antiferromagnetic Heisenberg spin chain, where a new state emerges with magnetization perpendicular to the polarization plane of the laser in place of the topologically ordered Haldane state. We then elucidate its physical mechanism by mapping the system to an effective static model. The theory also indicates that the phenomenon should occur in general quantum spin systems with a magnetic anisotropy. The required laser frequency is in the terahertz range, with the required intensity being within a prospective experimental feasibility.