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

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.

Laser-Driven Multiferroics and Ultrafast Spin Current Generation

“…This framework can also be applied to quantum magnets. Laser-induced magnetization growth in general quantum magnets [17,18] as well as laser-driven topological spin states [18,19], a quantum spin versions of Floquet topological insulators, were proposed recently.In the current work, we apply the Floquet theory to quantum multiferroics and study the synthetic interactions appearing in the effective Floquet Hamiltonian …”

Light-induced coherent magnon excitation in monolayer magnetic nanodots

“…The customary technique of dealing with the spin precession is the micromagnetics simulation [5][6][7][8] in which the magnetic component of light takes part in the the µth site has three components S µ = S x µ e x + S y µ e y + S σ µ e z with the quantum number s = 1. Here e x , e y and e z are the unit vectors of three coordinate axes.…”

Magnetization of a quantum spin system induced by a linear polarized laser

“…The idea explores the unitary transformation of the circularly polarized laser field to an effective magnetic field applied perpendicular to the polarization plane, with the effective magnitude of the magnetic field equal to the frequency of the laser. It was shown [8] that such a circular polarization is the key ingredient of the laser-induced magnetization of spin systems. In this study we propose to use the linear polarized laser applied to the spin system.…”

“…However, such a procedure requires very high magnetic fields, up to 100 T. On the other hand, a laser with a terahertz frequency can typically produce an effective magnetic field (after the unitary transformation, in the rotating frame) of the order of 40 T (while the magnitude of such a field is usually less than 0.5 T). Naturally, stronger effective fields can be obtained by increasing the frequency of the laser.Recently it was proposed to study magnetic systems under the action of high-frequency laser fields [8]. The idea explores the unitary transformation of the circularly polarized laser field to an effective magnetic field applied perpendicular to the polarization plane, with the effective magnitude of the magnetic field equal to the frequency of the laser.…”

“…Recently it was proposed to study magnetic systems under the action of high-frequency laser fields [8]. The idea explores the unitary transformation of the circularly polarized laser field to an effective magnetic field applied perpendicular to the polarization plane, with the effective magnitude of the magnetic field equal to the frequency of the laser.…”