Optimizing the proximity effect along the BCS-BEC crossover

TL;DR

This paper investigates how the proximity effect between two fermionic superfluids varies across the BCS-BEC crossover, using a non-local integral equation approach to optimize the pair penetration depth.

Contribution

It introduces a non-local integral equation method to analyze the proximity effect, avoiding boundary condition issues and allowing independent variation of coupling on both sides.

Findings

Identifies conditions for maximizing the pair penetration depth.

Provides temperature dependence of the proximity effect across the BCS-BEC crossover.

Shows how to optimize the proximity effect by tuning inter-particle couplings.

Abstract

The proximity effect, which arises at the interface between two fermionic superfluids with different critical temperatures, is examined with a non-local (integral) equation whose kernel contains information about the size of Cooper pairs that leak across the interface. This integral approach avoids reference to the boundary conditions at the interface that would be required with a differential approach. The temperature dependence of the pair penetration depth on the normal side of the interface is determined over a wide temperature range, also varying the inter-particle coupling along the BCS-BEC crossover independently on both sides of the interface. Conditions are found for which the proximity effect is optimized in terms of the extension of the pair penetration depth.