Photoemission spectrum and effect of inhomogeneous pairing fluctuations in the BCS-BEC crossover regime of an ultracold Fermi gas

TL;DR

This study analyzes the photoemission spectrum in a cold Fermi gas across the BCS-BEC crossover, emphasizing the role of inhomogeneous pairing fluctuations due to trapping potential, and successfully explains recent experimental observations.

Contribution

It introduces a comprehensive model including pairing fluctuations and trap effects to accurately interpret photoemission spectra in ultracold Fermi gases.

Findings

Inhomogeneous pairing fluctuations are crucial for understanding the spectrum.

Strong pairing fluctuations cause a pseudogap in the trap center.

The model's results align well with recent experimental data.

Abstract

We investigate the photoemission-type spectrum in a cold Fermi gas which was recently measured by JILA group [J. T. Stewart {\it et al}., Nature \textbf{454}, 744 (2008)]. This quantity gives us very useful information about single-particle properties in the BCS-BEC crossover. In this letter, including pairing fluctuations within a $T$-matrix theory, as well as effects of a harmonic trap within the local density approximation, we show that spatially inhomogeneous pairing fluctuations due to the trap potential is an important key to understand the observed spectrum. In the crossover region, while strong pairing fluctuations lead to the so-called pseudogap phenomenon in the trap center, such strong-coupling effects are found to be weak around the edge of the gas. Our results including this effect are shown to agree well with the recent photoemission data by JILA group.