Probing the Spectral Function Using Momentum Resolved Radio Frequency Spectroscopy in Trapped Fermi Gases

TL;DR

This paper demonstrates that momentum resolved RF spectroscopy effectively measures the fermionic spectral function in trapped Fermi gases, clarifying pairing signatures and revealing a smooth temperature dependence across the BCS-BEC crossover.

Contribution

It shows that momentum resolved RF probes can directly measure the spectral function and resolve ambiguities in interpreting RF experiments in ultracold Fermi gases.

Findings

Spectral function measurements are feasible with RF spectroscopy.

Temperature dependence of the spectral function is smooth across T_c.

Provides a clear dispersion signature of pairing phenomena.

Abstract

We address recent momentum resolved radio frequency (RF) experiments on ultracold trapped Fermi gases of $^{40}$K. We show that momentum resolved RF probes provide measurements of the centrally important fermionic spectral function. They also serve to remove ambiguity plaguing the interpretation of momentum integrated RF experiments by establishing a clear dispersion signature of pairing. We find that the temperature dependence of the spectral function is dramatic at unitarity, and, importantly, smooth from above to below $T_c$ throughout BCS-BEC crossover. This should be tested experimentally, given widespread predictions of first order behavior.