# Observation of wall-vortex composite defects in a spinor Bose-Einstein condensate

## TL;DR

This paper reports the experimental observation of wall-vortex composite defects in a spinor Bose-Einstein condensate, revealing their formation, dynamics, and nucleation mechanisms during phase transitions.

## Contribution

It provides the first direct observation of spin domain walls bounded by half-quantum vortices in a spin-1 BEC, demonstrating their formation and evolution during a controlled phase transition.

## Key findings

- Spin domain walls bounded by half-quantum vortices observed.
- Wall-vortex composite defects dynamically split due to snake instability.
- Singly charged quantum vortices form during strong quenches.

## Abstract

We report the observation of spin domain walls bounded by half-quantum vortices (HQVs) in a spin-1 Bose-Einstein condensate with antiferromagnetic interactions. A spinor condensate is initially prepared in the easy-plane polar phase, and then, suddenly quenched into the easy-axis polar phase. Domain walls are created via the spontaneous $\mathbb{Z}_2$ symmetry breaking in the phase transition and the walls dynamically split into composite defects due to snake instability. The end points of the defects are identified as HQVs for the polar order parameter and the mass supercurrent in their proximity is demonstrated using Bragg scattering. In a strong quench regime, we observe that singly charged quantum vortices are formed with the relaxation of free wall-vortex composite defects. Our results demonstrate a nucleation mechanism for composite defects via phase transition dynamics.