Berezinskii-Kosterlitz-Thouless transition of two-component Bose mixtures with inter-component Josephson coupling

TL;DR

This paper investigates the BKT transition in two-component Bose mixtures, revealing how inter-component coupling influences vortex behavior and transition characteristics, with implications for ultracold gases and superconductors.

Contribution

It demonstrates the effect of inter-component Josephson coupling on vortex binding and the number of BKT transitions in two-component Bose systems.

Findings

Decoupled phases exhibit two-step BKT transitions with half-quantized vortices.

Synchronized phases form molecule-antimolecule pairs, resulting in a single BKT transition.

Results are applicable to ultracold Bose mixtures and multiband superconductors.

Abstract

We study the Berezinskii-Kosterlitz-Thouless (BKT) transition of two-component Bose mixtures in two spatial dimensions. When phases of both components are decoupled, half-quantized vortex-antivortex pairs of each component induce two-step BKT transitions. On the other hand, when phases of the both components are synchronized through the inter-component Josephson coupling, two species of vortices of each component are bind to form a molecule, and in this case, we find that there is only one BKT transition by molecule-antimolecule pairs. Our results can be tested by two weakly-connected Bose systems such as two-component ultracold dilute Bose mixtures with the Rabi oscillation, and multiband superconductors.