Critical dynamics and phase transition of a strongly interacting warm spin-gas

TL;DR

This paper investigates a second-order phase transition in a warm cesium spin system driven by light, revealing critical behavior, phase diagram, and nonequilibrium dynamics, providing a platform for studying magnetic phase properties.

Contribution

It demonstrates the observation of critical phenomena and phase transition in a warm spin gas, including measurements of the phase diagram and critical slowing down, which is novel for such systems.

Findings

Observation of a second-order phase transition with macroscopic magnetization.

Power-law dependence of magnetization and divergence of susceptibility near phase boundary.

Critical slowing down of spin response exceeding five seconds near the transition.

Abstract

Phase transitions are emergent phenomena where microscopic interactions drive a disordered system into a collectively ordered phase. Near the boundary between two phases, the system can exhibit critical, scale-invariant behavior. Here, we report on a second-order phase transition accompanied by critical behavior in a system of warm cesium spins driven by linearly-polarized light. The ordered phase exhibits macroscopic magnetization when the interactions between the spins become dominant. We measure the phase diagram of the system and observe the collective behavior near the phase boundaries, including power-law dependence of the magnetization and divergence of the susceptibility. Out of equilibrium, we observe a critical slow-down of the spin response time by two orders of magnitude, exceeding five seconds near the phase boundary. This work establishes a controlled platform for investigating equilibrium and nonequilibrium properties of magnetic phases.