Pseudogap in fermionic density of states in the BCS-BEC crossover of atomic Fermi gases

TL;DR

This paper investigates the pseudogap phenomena in ultracold Fermi gases across the BCS-BEC crossover, revealing how the pseudogap and spectral features evolve with temperature and interaction strength.

Contribution

It provides a detailed analysis of the pseudogap behavior and introduces the temperatures $T^*$ and $T^{**}$ to characterize the pseudogap and spectral features in the crossover.

Findings

DOS exhibits a pseudogap near unitarity

Pseudogap temperature $T^*$ is identified where DOS pseudogap disappears

Spectral weight double-peak structure vanishes at $T^{**}$

Abstract

We study pseudogap behaviors of ultracold Fermi gases in the BCS-BEC crossover region. We calculate the density of states (DOS), as well as the single-particle spectral weight, above the superfluid transition temperature $T_{\rm c}$ including pairing fluctuations within a $T$-matrix approximation. We find that DOS exhibits a pseudogap structure in the BCS-BEC crossover region, which is most remarkable near the unitarity limit. We determine the pseudogap temperature $T^*$ at which the pseudogap structure in DOS disappears. We also introduce another temperature $T^{**}$ at which the BCS-like double-peak structure disappears in the spectral weight. While one finds $T^*>T^{**}$ in the BCS regime, $T^{**}$ becomes higher than $T^*$ in the crossover and BEC regime. We also determine the pseudogap region in the phase diagram in terms of temperature and pairing interaction.