Environment-controlled Floquet-state paramagnetism

TL;DR

This paper investigates how strong oscillating magnetic fields and thermal environments influence the magnetization of ideal spin systems, revealing sign changes and enhanced magnetization due to Floquet states, with implications for nonequilibrium thermodynamics.

Contribution

It demonstrates the dependence of magnetization sign and magnitude on driving amplitude and system-bath coupling, highlighting novel effects in Floquet-state driven spin systems.

Findings

Magnetization sign depends on the amplitude of the oscillating field.

Absolute magnetization can exceed equilibrium values.

System-bath coupling influences Floquet-state occupations.

Abstract

We study the response of ideal spin systems which are interacting with both a strong oscillating magnetic field, and a thermal environment, to a weak probing magnetic field. We demonstrate that even the sign of the resulting mean magnetization depends on the amplitude of the driving field, and that its absolute value can be significantly larger than the equilibrium magnetization in the absence of time-periodic forcing. Since the underlying Floquet-state occupation probabilities are determined by the precise form of the system-bath coupling, future measurements of such effects have the potential to establish a particularly innovative line of research, providing information on nonequilibrium thermodynamics, and giving access to quantities which usually remain hidden when probing equilibrium systems.