# Superfluid density and critical velocity near the fermionic Berezinskii-Kosterlitz-Thouless transition

## TL;DR

This paper provides a theoretical analysis of superfluid density and critical velocity near the Berezinskii-Kosterlitz-Thouless transition in a 2D strongly interacting Fermi gas, proposing experimental detection methods.

## Contribution

It introduces a Gaussian pair fluctuation approach to calculate superfluid properties and suggests a practical experimental setup to observe the transition.

## Key findings

- Calculated superfluid density and critical temperature at BKT transition
- Predicted a measurable jump in Landau critical velocity during experiments
- Proposed stirring method to detect superfluid-normal interface

## Abstract

We theoretically investigate superfluidity in a strongly interacting Fermi gas confined to two dimensions at finite temperature. Using a Gaussian pair fluctuation theory in the superfluid phase, we calculate the superfluid density and determine the critical temperature and chemical potential at the Berezinskii-Kosterlitz-Thouless transition. We propose that the transition can be unambiguously demonstrated in cold-atom experiments by stirring the superfluid Fermi gas using a red detuned laser beam, to identify the characteristic jump in the local Landau critical velocity at the superfluid-normal interface, as the laser beam moves across the cloud.