Coarsening and thermalisation properties of a quenched ferromagnetic spin-1 condensate

TL;DR

This paper investigates the non-equilibrium dynamics and domain growth in a quenched ferromagnetic spin-1 condensate, revealing phase-dependent coarsening behavior and thermalization processes through analytic models and topological defect analysis.

Contribution

It introduces a unified framework for understanding scale-invariant domain growth and topological defects in different ferromagnetic phases of spin-1 condensates after a quench.

Findings

Single dynamical critical exponent for each phase

Analytic models accurately predict coarsening exponents

Distinct domain structures and defects in easy-axis and easy-plane phases

Abstract

We examine the dynamics of a quasi-two-dimensional spin-1 condensate in which the quadratic Zeeman energy q is suddenly quenched to a value where the system has a ferromagnetic ground state. There are two distinct types of ferromagnetic phases, i.e. a range of q values where the magnetization prefers to be in the direction of the external field (easy-axis), and a range of q values where it prefers to be transverse to the field (easy-plane). We study the quench dynamics for a variety of q values and show that there is a single dynamical critical exponent to characterize the scale invariant domain growth for each ferromagnetic phase. For both quenches we give simple analytic models that capture the essential scale invariant dynamics, and correctly predict the exponents. Because the order parameter for each phase is different, the natures of the domains and the relevant topological defects in each type of coarsening is also different. To explore these differences we characterize the fractal dimension of the domain walls, and the relationship of polar-core spin vortices to the domains in the easy-plane phase. Finally, we consider how the energy liberated from the quench thermalizes in the easy-axis quench. We show that local equilibrium is established in the spin waves on moderate time scales, but continues to evolve as the domains anneal.