Superfluid density of states and pseudogap phenomenon in the BCS-BEC crossover regime of a superfluid Fermi gas

TL;DR

This paper explores how the pseudogap evolves into the superfluid gap across the BCS-BEC crossover in a superfluid Fermi gas, revealing the role of pairing fluctuations and providing insights into strong-coupling phenomena.

Contribution

It provides a detailed analysis of the evolution of the pseudogap into the superfluid gap using a $T$-matrix approach across the entire BCS-BEC crossover.

Findings

Pseudogap in DOS evolves into the superfluid gap in the weak-coupling regime.

Superfluid gap appears after pseudogap disappears in the crossover region.

Identifies the region dominated by strong pairing fluctuations in the phase diagram.

Abstract

We investigate single-particle excitations and strong-coupling effects in the BCS-BEC crossover regime of a superfluid Fermi gas. Including phase and amplitude fluctuations of the superfluid order parameter within a $T$-matrix theory, we calculate the superfluid density of states (DOS), as well as single-particle spectral weight, over the entire BCS-BEC crossover region below the superfluid transition temperature $T_{\rm c}$. We clarify how the pseudogap in the normal state evolves into the superfluid gap, as one passes through $T_{\rm c}$. While the pseudogap in DOS continuously evolves into the superfluid gap in the weak-coupling BCS regime, the superfluid gap in the crossover region is shown to appear in DOS after the pseudogap disappears below $T_{\rm c}$. In the phase diagram with respect to the temperature and interaction strength, we determine the region where strong pairing fluctuations dominate over single-particle properties of the system. Our results would be useful for the study of strong-coupling phenomena in the BCS-BEC crossover regime of a superfluid Fermi gas.