Density and spin response functions in ultracold fermionic atom gases

TL;DR

This paper introduces a novel method to detect superfluidity in ultracold fermionic gases by analyzing density and spin response functions, providing clear signatures of the BEC-BCS crossover and spin symmetry breaking.

Contribution

It presents a new measurement approach using two-body correlation functions to distinguish normal and anomalous densities in ultracold fermionic gases.

Findings

Sign change in density response function indicates BEC-BCS transition.

Measurement of response functions can separately access normal and anomalous densities.

Predicted spin rotational symmetry-breaking in the system.

Abstract

We propose a new method of detecting the onset of superfluidity in a two-component ultracold fermionic gas of atoms governed by an attractive short-range interaction. By studying the two-body correlation functions we find that a measurement of the momentum distribution of the density and spin response functions allows one to access separately the normal and anomalous densities. The change in sign at low momentum transfer of the density response function signals the transition between a BEC and a BCS regimes, characterized by small and large pairs, respectively. This change in sign of the density response function represents an unambiguous signature of the BEC to BCS crossover. Also, we predict spin rotational symmetry-breaking in this system.