Fulde-Ferrell-Larkin-Ovchinnikov state induced by antiferromagnetic order in $\kappa$-type organic conductors

TL;DR

This paper theoretically demonstrates that antiferromagnetic order in quasi-two-dimensional organic conductors can induce a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconducting state with finite momentum pairs, without external magnetic fields.

Contribution

It reveals a novel mechanism for FFLO state formation driven by intrinsic magnetic order in organic superconductors, expanding understanding of unconventional superconductivity.

Findings

Antiferromagnetic order can induce FFLO state in organic conductors.

The FFLO state can occur without external magnetic fields.

Theoretical confirmation via effective models and many-body calculations.

Abstract

We theoretically investigate superconductivity under a spin-split band structure owing to a collinear-type antiferromagnetic order in quasi-two-dimensional organic compounds $\kappa$-(BEDT-TTF)$_2X$. We find that the magnetic order can induce a Fulde--Ferrell--Larkin--Ovchinnikov (FFLO) state, where the Cooper pair possesses a finite center-of-mass momentum. We show this from two types of analyses: (1) an effective model where simple intraband attractive interactions are assumed, and (2) many-body calculations of the repulsive Hubbard model based on the fluctuation-exchange approximation and the linearized Eliashberg equation. Our results show the possibility of realizing the FFLO state without applying an external magnetic field.