# Coupled superfluidity of binary Bose mixtures in two dimensions

## TL;DR

This paper investigates how inter-species interactions in a two-dimensional binary Bose gas modify the BKT transition, revealing a locking of superfluid critical temperatures due to vortex interactions mediated by nondissipative drag.

## Contribution

It extends the BKT theory to two-component Bose gases, incorporating the effects of nondissipative drag and vortex interactions on superfluid phase transitions.

## Key findings

- Inter-species interactions induce nondissipative drag between superfluid components.
- Vortex unbinding in one component can cause superfluid breakdown in the other.
- Superfluid critical temperatures can become locked due to vortex-mediated coupling.

## Abstract

We consider a two-component Bose gas in two dimensions at low temperature with short-range repulsive interaction. In the coexistence phase where both components are superfluid, inter-species interactions induce a nondissipative drag between the two superfluid flows (Andreev-Bashkin effect). We show that this behavior leads to a modification of the usual Berezinskii-Kosterlitz-Thouless (BKT) transition in two dimensions. We extend the renormalization of the superfluid densities at finite temperature using the renormalization group approach and find that the vortices of one component have a large influence on the superfluid properties of the other, mediated by the nondissipative drag. The extended BKT flow equations indicate that the occurrence of the vortex unbinding transition in one of the components can induce the breakdown of superfluidity also in the other, leading to a locking phenomenon for the critical temperatures of the two gases.