On the theory of the vortex state in the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase

TL;DR

This paper investigates how the vortex state in the FFLO phase varies with magnetic field orientation, providing numerical analysis of the upper critical field and discussing phase transition mechanisms, especially in CeCoIn5.

Contribution

It offers a detailed numerical analysis of the vortex state in the FFLO phase considering field orientation and order parameter modulation, including a general scheme for anisotropic superconductors.

Findings

Vortex state varies significantly with field orientation.

Transitions between different mixed states are prominent in the FFLO phase.

First-order phase transition mechanisms are discussed for CeCoIn5.

Abstract

We demonstrate that the vortex state in the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase may be very different depending on the field orientation relative to the crystalline axes. We calculate numerically the upper critical field near the tricritical point taking into account the modulation of the order parameter along the magnetic field as well as the higher Landau levels. For s-wave superconductors with the anisotropy described by an elliptical Fermi surface we propose a general scheme of the analysis of the angular dependence of upper critical field at all temperatures on the basis of the exact solution for the order parameter. Our results show that the transitions (with tilting magnetic field) between different types of mixed states may be a salient feature of the FFLO phase. Moreover we discuss the reasons for the first-order phase transition into the FFLO state in the case of CeCoIn5 compound.