Kosterlitz-Thouless transition and vortex-antivortex lattice melting in two-dimensional Fermi gases with $p$- or $d$-wave pairing

TL;DR

This paper theoretically investigates the finite-temperature Kosterlitz-Thouless and vortex-antivortex lattice melting transitions in two-dimensional Fermi gases with p- or d-wave pairing, revealing how these transitions evolve across the BCS-BEC crossover.

Contribution

It provides a detailed analysis of KT and VAL transitions in 2D Fermi gases with unconventional pairing, including effects of interaction strength and Fermi surface mismatch, which was not previously explored.

Findings

KT and VAL transition temperatures increase across the BCS-BEC transition.

Transition temperatures approach constant values in the deep BEC regime.

Non-analyticities in chemical potential and superfluid parameters characterize the BCS-BEC transition.

Abstract

We present a theoretical study of the finite-temperature Kosterlitz-Thouless (KT) and vortex-antivortex lattice (VAL) melting transitions in two-dimensional Fermi gases with $p$- or $d$-wave pairing. For both pairings, when the interaction is tuned from weak to strong attractions, we observe a quantum phase transition from the Bardeen-Cooper-Schrieffer (BCS) superfluidity to the Bose-Einstein condensation (BEC) of difermions. The KT and VAL transition temperatures increase during this BCS-BEC transition and approach constant values in the deep BEC region. The BCS-BEC transition is characterized by the non-analyticities of the chemical potential, the superfluid order parameter, and the sound velocities as functions of the interaction strength at both zero and finite temperatures; however, the temperature effect tends to weaken the non-analyticities comparing to the zero temperature case. The effect of mismatched Fermi surfaces on the $d$-wave pairing is also studied.