Pseudogap temperature and effects of a harmonic trap in the BCS-BEC crossover regime of an ultracold Fermi gas

TL;DR

This paper theoretically studies the pseudogap phenomena in a trapped ultracold Fermi gas across the BCS-BEC crossover, analyzing how pseudogap features evolve with temperature and interaction strength using a combined T-matrix and local density approximation approach.

Contribution

It introduces a method to determine pseudogap temperatures in a trapped Fermi gas and explains recent experimental observations as pseudogap effects, advancing understanding of normal state properties.

Findings

Identification of pseudogap temperatures T* and T** across the BCS-BEC crossover.

Explanation of the back-bending peak in photoemission spectra as a pseudogap effect.

Analysis of how pseudogap structures disappear with increasing temperature.

Abstract

We theoretically investigate excitation properties in the pseudogap regime of a trapped Fermi gas. Using a combined $T$-matrix theory with the local density approximation, we calculate strong-coupling corrections to single-particle local density of states (LDOS), as well as the single-particle local spectral weight (LSW). Starting from the superfluid phase transition temperature $T_{\rm c}$, we clarify how the pseudogap structures in these quantities disappear with increasing the temperature. As in the case of a uniform Fermi gas, LDOS and LSW give different pseudogap temperatures $T^*$ and $T^{**}$ at which the pseudogap structures in these quantities completely disappear. Determining $T^*$ and $T^{**}$ over the entire BCS (Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein condensate) crossover region, we identify the pseudogap regime in the phase diagram with respect to the temperature and the interaction strength. We also show that the so-called back-bending peak recently observed in the photoemission spectra by JILA group may be explained as an effect of pseudogap phenomenon in the trap center. Since strong pairing fluctuations, spatial inhomogeneity, and finite temperatures, are important keys in considering real cold Fermi gases, our results would be useful for clarifying normal state properties of this strongly interacting Fermi system.