The Josephson effect throughout the BCS-BEC crossover

TL;DR

This paper investigates the Josephson effect in fermionic superfluids across the BCS-BEC crossover, revealing enhanced currents near unitarity and proposing a method to determine the pairing gap from critical current measurements.

Contribution

It provides a numerical analysis of the Josephson effect across the BCS-BEC crossover and introduces a new procedure to extract the pairing gap from critical current data.

Findings

Josephson current is enhanced near unitarity.

Critical current approaches Landau limit depending on coupling.

Method to extract pairing gap from critical current.

Abstract

We study the stationary Josephson effect for neutral fermions across the BCS-BEC crossover, by solving numerically the Bogoliubov-de Gennes equations at zero temperature. The Josephson current is found to be considerably enhanced for all barriers at about unitarity. For vanishing barrier, the Josephson critical current approaches the Landau limiting value which, depending on the coupling, is determined by either pair-breaking or sound-mode excitations. In the coupling range from the BCS limit to unitarity, a procedure is proposed to extract the pairing gap from the Landau limiting current.