Theory of Photoemission-type Experiment in the BCS-BEC Crossover Regime of a Superfluid Fermi Gas

TL;DR

This paper provides a theoretical analysis of photoemission experiments in ultracold Fermi gases, demonstrating the detectability of the pseudogap and its evolution into the superfluid gap across the BCS-BEC crossover.

Contribution

It introduces a strong-coupling $T$-matrix theoretical framework including trap effects to interpret photoemission spectra in the crossover regime.

Findings

Current experiments can detect the pseudogap phenomenon.

The pseudogap evolves into a superfluid gap below the transition temperature.

Theoretical spectra match experimental observations in the BCS-BEC crossover.

Abstract

We theoretically investigate the recent photoemission-type experiment on $^{40}$K Fermi gases done by JILA group. Including pairing fluctuations within a strong-coupling $T$-matrix theory, as well as effects of a harmonic trap within the local density approximation, we calculate photoemission spectra in the BCS (Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein condensation) crossover region. We show that the energy resolution of the current photoemission experiment is enough to detect the pseudogap phenomenon. We also show how the pseudogap in single-particle excitations continuously changes into the superfluid gap, as one decreases the temperature below the superfluid phase transition temperature. Our results would be useful for the study of single-particle properties of ultracold Fermi gases in the BCS-BEC crossover.