Fulde-Ferrell-Larkin-Ovchinnikov States and Topological Bogoliubov Fermi Surfaces in Altermagnets: an Analytical Study

TL;DR

This paper analytically explores the phase diagram of a 2D spin-1/2 Fermi gas with altermagnetic spin splitting, revealing four phases including unconventional superconducting states like FFLO and topological Bogoliubov Fermi surfaces.

Contribution

It provides the first analytical characterization of FFLO and TBFS phases in altermagnets, highlighting the role of altermagnetic spin splitting in exotic pairing phenomena.

Findings

Identification of four distinct phases in the model

Demonstration of FFLO and TBFS as unconventional superconducting states

Provision of a theoretical framework for experimental realization

Abstract

We present an analytical study of the ground-state phase diagram for dilute two-dimensional spin-1/2 Fermi gases exhibiting $d$-wave altermagnetic spin splitting under $s$-wave pairing. Within the Bogoliubov-de Gennes mean-field framework, four distinct phases are identified: a Bardeen-Schrieffer-Cooper-type superfluid, a normal metallic phase, a nodal superfluid with topological Bogoliubov Fermi surfaces (TBFSs), and Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states with finite center-of-mass momentum. Among these, the FFLO states and TBFSs exemplify two unconventional forms of superconductivity. Considering the simplicity of this model, with only one band, zero net magnetization, and $s$-wave paring, the emergence of both unconventional phases underscores the pivotal role of altermagnetic spin splitting in enabling exotic pairing phenomena. This analytical study not only offers a valuable benchmark for future numerical simulations, but also provides a concrete experimental roadmap for realizing FFLO states and TBFSs in altermagnets.