Evolution of an isolated monopole in a spin-1 Bose-Einstein condensate

TL;DR

This paper simulates the decay of an isolated monopole in a spin-1 Bose-Einstein condensate, revealing spontaneous transformations of topological defects during phase transitions driven by intrinsic interactions.

Contribution

It demonstrates the decay mechanisms of monopoles without external fields and characterizes the resulting vortex structures, advancing understanding of topological defect dynamics in quantum gases.

Findings

Monopoles decay into polar-core spin vortices during phase transition.

Monopoles pierced by vortices decay into specific vortex types depending on winding number.

Resulting vortices are encircled by polar-core vortex rings.

Abstract

We simulate the decay dynamics of an isolated monopole defect in the nematic vector of a spin-1 Bose-Einstein condensate during the polar-to-ferromagnetic phase transition of the system. Importantly, the decay of the monopole occurs in the absence of external magnetic fields and is driven principally by the dynamical instability due to the ferromagnetic spin-exchange interactions. An initial isolated monopole is observed to relax into a polar-core spin vortex, thus demonstrating the spontaneous transformation of a point defect of the polar order parameter manifold to a line defect of the ferromagnetic manifold. We also investigate the dynamics of an isolated monopole pierced by a quantum vortex line with winding number k. It is shown to decay into a coreless Anderson-Toulouse vortex if k = 1 and into a singular vortex with an empty core if k = 2. In both cases, the resulting vortex is also encircled by a polar-core vortex ring.