Vortex molecules in coherently coupled two-component Bose-Einstein condensates

TL;DR

This paper predicts and analyzes vortex molecules in rotating two-component Bose-Einstein condensates with coherent internal state coupling, revealing their structure, binding mechanism, and effects of anisotropy on vortex lattice formation.

Contribution

It introduces the concept of vortex molecules in coupled BECs, detailing their structure, binding mechanism, and the impact of scattering length differences on their anisotropy.

Findings

Vortex molecules connect vortices in different components via domain walls.

The binding mechanism is explained using a nonlinear sigma model and variational approach.

Anisotropy in vortex molecules causes distorted vortex lattices in fast rotation.

Abstract

A vortex molecule is predicted in rotating two-component Bose-Einstein condensates whose internal hyperfine states are coupled coherently by an external field. A vortex in one component and that in the other are connected by a domain wall of the relative phase, constituting a "vortex molecule", which features a nonaxisymmetric (pseudo)spin texture with a pair of merons. The binding mechanism of the vortex molecule is discussed based on a generalized nonlinear sigma model and a variational ansatz. The anisotropy of vortex molecules is caused by the difference in the scattering lengths, yielding a distorted vortex-molecule lattice in fast rotating condensates.