Signatures of superfluidity for Feshbach-resonant Fermi gases

TL;DR

This paper proposes a method to detect superfluidity in Feshbach-resonant Fermi gases by analyzing the asymmetry and broadening of peaks in atom transfer spectra, revealing the transition from pseudogap to superfluid state.

Contribution

It introduces a spectroscopic technique to identify superfluid transition signatures in Fermi gases across the BCS-BEC crossover, accounting for pseudogap effects.

Findings

Peak asymmetry correlates with superfluid transition.

Broadening decreases below critical temperature.

Spectroscopic signatures distinguish pseudogap from superfluidity.

Abstract

We consider atomic Fermi gases where Feshbach resonances can be used to continuously tune the system from weak to strong interaction regime, allowing to scan the whole BCS-BEC crossover. We show how a probing field transferring atoms out of the superfluid can be used to detect the onset of the superfluid transition in the high-$T_c$ and BCS regimes. The number of transferred atoms, as a function of the energy given by the probing field, peaks at the gap energy. The shape of the peak is asymmetric due to the single particle excitation gap. Since the excitation gap includes also a pseudogap contribution, the asymmetry alone is not a signature of superfluidity. Incoherent nature of the non-condensed pairs leads to broadening of the peak. The pseudogap and therefore the broadening decay below the critical temperature, causing a drastic increase in the asymmetry. This provides a signature of the transition.