Establishing the Presence of Coherence in Atomic Fermi Superfluids: Spin-Flip and Spin-Preserving Bragg Scattering at Finite Temperatures

TL;DR

This paper proposes using the difference in finite temperature structure factors for spin and density to identify superfluidity in ultracold Fermi gases, applicable across the BCS-BEC crossover.

Contribution

It introduces a method to detect superfluidity via spin and density structure factors, incorporating conservation laws for accurate finite temperature analysis.

Findings

Finite temperature structure factor differences indicate superfluidity.

Method applicable across various scattering lengths.

Provides a direct experimental approach for superfluidity detection.

Abstract

We show how the difference between the finite temperature T structure factors, called S_-, associated with spin and density, can be used as a indication of superfluidity in ultracold Fermi gases. This observation can be exploited in two photon Bragg scattering experiments on gases which undergo BCS- Bose Einstein condensation crossover. Essential to our calculations is a proper incorporation of spin and particle number conservation laws which lead to compatibility at general T with two f-sum rules. Because it is applicable to general scattering lengths, a measurement of S- can be a useful, direct approach for establishing where superfluidity occurs.