Unconventional superconducting phases in a correlated two-dimensional Fermi gas of nonstandard quasiparticles: a simple model

TL;DR

This paper explores a model of a 2D correlated Fermi gas with spin-dependent masses, revealing complex phase transitions between BCS and FFLO superconducting states influenced by magnetic fields and temperature.

Contribution

It introduces a simple model demonstrating how spin-dependent quasiparticle masses stabilize FFLO phases in 2D superconductors, highlighting their robustness against BCS states.

Findings

Multiple phase transitions between BCS and FFLO states depending on H_a and T.

Identification of two distinct FFLO phases and reentrant behavior at high fields.

Enhanced stability of FFLO phases due to spin-dependent masses compared to Landau quasiparticles.

Abstract

We discuss a detailed phase diagram and other microscopic characteristics on the applied magnetic field - temperature (H_a-T) plane for a simple model of correlated fluid represented by a two-dimensional (2D) gas of heavy quasiparticles with masses dependent on the spin direction and the effective field generated by the electron correlations. The consecutive transitions between the Bardeen-Cooper-Schrieffer (BCS) and the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phases are either continuous or discontinuous, depending on the values of H_a and T. In the latter case, weak metamagnetic transitions occur at the BCS-FFLO boundary. We single out two different FFLO phases, as well as a reentrant behaviour of one of them at high fields. The results are compared with those for ordinary Landau quasiparticles in order to demonstrate the robustness of the FFLO states against the BCS state for the case with spin-dependent masses (SDM). We believe that the mechanism of FFLO stabilization by SDM is generic: other high-field low-temperature (HFLT) superconducting phases benefit from SDM as well.