Larkin-Ovchinnikov-Fulde-Ferrell state in quasi-one-dimensional superconductors

TL;DR

This paper explores the phase diagram of quasi-one-dimensional superconductors under magnetic fields, highlighting conditions for the LOFF state and its experimental signatures, especially in Bechgaard salts and related organic materials.

Contribution

It provides a detailed theoretical analysis of the LOFF state in quasi-1D superconductors, including phase diagrams and experimental implications, emphasizing the role of anisotropy.

Findings

High-field superconducting phases are stabilized by dimensional crossover.

Experimental data on (TMTSF)$_2$ClO$_4$ align with theoretical predictions.

Large anisotropy enhances the likelihood of observing the LOFF state.

Abstract

The properties of a quasi-one-dimensional (quasi-1D) superconductor with {\it an open Fermi surface} are expected to be unusual in a magnetic field. On the one hand, the quasi-1D structure of the Fermi surface strongly favors the formation of a non-uniform state (Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) state) in the presence of a magnetic field acting on the electron spins. On the other hand, a magnetic field acting on an open Fermi surface induces a dimensional crossover by confining the electronic wave-functions wave-functions along the chains of highest conductivity, which results in a divergence of the orbital critical field and in a stabilization at low temperature of a cascade of superconducting phases separated by first order transistions. In this paper, we study the phase diagram as a function of the anisotropy. We discuss in details the experimental situation in the quasi-1D organic conductors of the Bechgaard salts family and argue that they appear as good candidates for the observation of the LOFF state, provided that their anisotropy is large enough. Recent experiments on the organic quasi-1D superconductor (TMTSF)$_2$ClO$_4$ are in agreement with the results obtained in this paper and could be interpreted as a signature of a high-field superconducting phase. We also point out the possibility to observe a LOFF state in some quasi-2D organic superconductors.