Phase Fluctuations and Kosterlitz-Thouless Transition in Two-Dimensional Fulde-Ferrell-Larkin-Ovchinnikov Superconductors

TL;DR

This paper investigates how phase fluctuations affect the stability of FFLO superconducting states in two-dimensional systems, revealing that certain ordered states are suppressed at finite temperatures while others can sustain quasi-long-range order.

Contribution

It provides a theoretical analysis of phase fluctuation effects on FFLO states in 2D superconductors using a generalized Ginzburg-Landau framework, highlighting conditions for stability.

Findings

Single-direction FFLO states lack long-range and quasi-long-range order at finite temperatures.

Lattice-structured FFLO states can maintain quasi-long-range order similar to BCS states.

Fermi surface and pairing anisotropy influence the stability of FFLO states.

Abstract

Effect of the phase fluctuations of the order parameter on the stability of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states are examined in exactly two-dimensional (2D) type-II superconductors with cylindrically symmetric Fermi surface on the basis of a generalized Ginzburg-Landau theory. It is found that for the FFLO states with oscillations in a single direction, not only the long-range order but also quasi-long-range order (QLRO), which is characterized by a power law decay of the order parameter correlation function, is suppressed by the phase fluctuations at any finite temperatures. On the other hand, for the FFLO states with order parameter structures such as triangular and square lattices, it is shown that the QLRO is possible as the uniform BCS state. Systems with anisotropy in the Fermi surface and pairing are also discussed.