Relativistic BCS-BEC crossover of a two-species Fermi gas with number density asymmetry at zero temperature

TL;DR

This paper explores the relativistic BCS-BEC crossover in a two-species Fermi gas with density imbalance at zero temperature, revealing phase transitions, stability conditions, and the emergence of a relativistic BEC state.

Contribution

It introduces a comprehensive analysis of relativistic effects and phase stability in asymmetric two-species Fermi gases, extending nonrelativistic BCS-BEC crossover understanding.

Findings

Identification of a relativistic BEC state at strong attraction

Observation of gapless antifermion excitations

Phase diagrams showing stability regions and phase separation

Abstract

We systematically study relativistic two-species fermions with tunable attractive interactions and number-density asymmetry at zero temperature. In general, a Bardeen-Cooper-Schrieffer (BCS) - Bose-Einstein Condensation (BEC) - relativistic BEC (RBEC) crossover is observed. A generalized BCS ground state and its stability are analyzed. The homogeneous superfluid phase can become unstable and we consider phase separation in real space for neutral systems. In the nonrelativistic limit, our results are consistent with well-known results. In addition to a BCS-BEC crossover similar to that in the nonrelativistic case, in the strongly attractive regime gapless excitations of antifermions and a RBEC state are observed. We address how different phases respond to number density asymmetry and present predictive phase diagrams of BCS-BEC-RBEC crossover.