Pseudogap effects in the strongly correlated regime of the two-dimensional Fermi gas

TL;DR

This study uses advanced quantum Monte Carlo methods to explore pseudogap phenomena in a strongly correlated two-dimensional Fermi gas, revealing pairing correlations above the superfluid transition temperature.

Contribution

It provides controlled, systematic calculations of thermodynamic properties and pseudogap signatures in the strongly correlated regime of 2D Fermi gases, extending understanding of pairing above $T_c$.

Findings

Pseudogap signatures observed above $T_c$ in spin susceptibility and free-energy gap.

Finite-size scaling used to estimate critical temperature $T_c$.

Results include thermodynamic properties like the contact in the strongly correlated regime.

Abstract

The two-species Fermi gas with attractive short-range interactions in two spatial dimensions provides a paradigmatic system for the understanding of strongly correlated Fermi superfluids in two dimensions. It is known to exhibit a BEC-BCS crossover as a function of $\ln(k_F a)$, where $a$ is the scattering length, and to undergo a Berezinskii-Kosterlitz-Thouless superfluid transition below a critical temperature $T_c$. However, the extent of a pseudogap regime in the strongly correlated regime of $\ln(k_F a)\sim 1$, in which pairing correlations persist above $T_c$, remains largely unexplored with controlled theoretical methods. Here we use finite-temperature auxiliary-field quantum Monte Carlo (AFMC) methods on discrete lattices in the canonical ensemble formalism to calculate thermodynamical observables in the strongly correlated regime. We extrapolate to continuous time and the continuum limit to eliminate systematic errors and present results for particle numbers ranging from $N=42$ to $N=162$. We estimate $T_c$ by a finite-size scaling analysis, and observe clear pseudogap signatures above $T_c$ and below a temperature $T^*$ in both the spin susceptibility and free-energy gap. We also present results for the contact, a fundamental thermodynamic property of quantum many-body systems with short-range interactions.