Unconventional pairing in few-fermion systems at finite temperature

TL;DR

This paper investigates how finite temperature affects pairing correlations in one-dimensional two-component fermionic systems, revealing a crossover from FFLO to BCS pairing with increasing temperature, using exact diagonalization and density correlation analysis.

Contribution

It provides a detailed analysis of temperature-induced pairing crossovers in imbalanced fermionic systems confined in 1D traps, highlighting the transition from FFLO to BCS states.

Findings

Imbalanced systems exhibit a crossover from FFLO to BCS pairing with increasing temperature.

Phase diagram boundary between FFLO and BCS phases is approximately determined.

Density and noise correlations reveal non-classical pairing behaviors.

Abstract

Attractively interacting two-component mixtures of fermionic particles confined in a one-dimensional harmonic trap are investigated. Properties of balanced and imbalanced systems are systematically explored with the exact diagonalization approach, focusing on the finite-temperature effects. Using single- and two-particle density distributions, specific non-classical pairing correlations are analyzed in terms of the noise correlations -- quantity directly accessible in state-of-the-art experiments with ultra-cold atoms. It is shown that along with increasing temperature, any imbalanced system hosting Fulde-Ferrel-Larkin-Ovchinnikov pairs crossovers to a standard Bardeen-Cooper-Schrieffer one characterized by zero net momentum of resulting pairs. By performing calculations for systems with different imbalances, the approximate boundary between the two phases on a phase diagram is determined.