Low-dimensional pairing fluctuations and pseudogapped photoemission spectrum in a trapped two-dimensional Fermi gas

TL;DR

This paper studies how pairing fluctuations in a trapped two-dimensional Fermi gas cause pseudogap phenomena and double-peak structures in photoemission spectra, aligning well with recent experimental observations.

Contribution

It demonstrates the impact of low-dimensional pairing fluctuations on single-particle spectra using a combined T-matrix and local density approximation approach.

Findings

Local density of states shows a dip in the trap center.

Pseudogap leads to a double peak in photoemission spectrum.

Results agree with recent experimental data on 2D Fermi gases.

Abstract

We investigate strong-coupling properties of a trapped two-dimensional normal Fermi gas. Within the framework of a combined $T$-matrix theory with the local density approximation, we calculate the local density of states, as well as the photoemission spectrum, to see how two-dimensional pairing fluctuations affect these single-particle quantities. In the BCS (Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein condensation) crossover region, we show that the local density of states exhibits a dip structure in the trap center, which is more remarkable than the three-dimensional case. This pseudogap phenomenon is found to naturally lead to a double peak structure in the photoemission spectrum. The peak-to-peak energy of the spectrum at p=0 agrees well with the recent experiment on a two-dimensional 40K Fermi gas [M. Feld, et al., Nature 480, 75 (2011)]. Since pairing fluctuations are sensitive to the dimensionality of a system, our results would be useful for the study of many-body physics in the BCS-BEC crossover regime of a two-dimensional Fermi gas.