BCS-BEC crossover in a two-dimensional Fermi gas

TL;DR

This paper uses quantum Monte Carlo simulations to study the BCS-BEC crossover in a 2D Fermi gas at zero temperature, revealing significant deviations from mean-field theory and emphasizing the importance of interaction effects.

Contribution

It provides non-mean-field calculations of the equation of state, gap, and Tan's contact parameter across the BCS-BEC crossover in two dimensions.

Findings

Large deviations from mean-field predictions in the BEC regime

Significant role of dimer-dimer and atom-dimer interactions

Quantitative results for Tan's contact parameter

Abstract

We investigate the crossover from Bardeen-Cooper-Schrieffer (BCS) superfluidity to Bose-Einstein condensation (BEC) in a two-dimensional Fermi gas at T=0 using the fixed-node diffusion Monte Carlo method. We calculate the equation of state and the gap parameter as a function of the interaction strength, observing large deviations compared to mean-field predictions. In the BEC regime our results show the important role of dimer-dimer and atom-dimer interaction effects that are completely neglected in the mean-field picture. Results on Tan's contact parameter associated with short-range physics are also reported along the BCS-BEC crossover.