A Two-dimensional Superconductor in a Tilted Magnetic Field - new states with finite Cooper-pair momentum

TL;DR

This paper investigates novel superconducting states with finite Cooper-pair momentum in layered superconductors under tilted magnetic fields, revealing complex order parameter structures and magnetic responses near the critical field.

Contribution

It introduces a detailed analysis of superconducting states with finite momentum in tilted fields, including stable structures and magnetic properties, extending understanding of FFLO states.

Findings

States with coexisting vortices and antivortices identified

Magnetic response varies between diamagnetic and paramagnetic

Transition from Landau levels to FFLO states analyzed

Abstract

Varying the angle Theta between applied field and the conducting planes of a layered superconductor in a small interval close to the plane-parallel field direction, a large number of superconducting states with unusual properties may be produced. For these states, the pair breaking effect of the magnetic field affects both the orbital and the spin degree of freedom. This leads to pair wave functions with finite momentum, which are labeled by Landau quantum numbers 0<n<\infty. The stable order parameter structure and magnetic field distribution for these states is found by minimizing the quasiclassical free energy near H_{c2} including nonlinear terms. One finds states with coexisting line-like and point-like order parameter zeros and states with coexisting vortices and antivortices. The magnetic response may be diamagnetic or paramagnetic depending on the position within the unit cell. The structure of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states at Theta=0 is reconsidered. The transition n->\infty of the paramagnetic vortex states to the FFLO-limit is analyzed and the physical reason for the occupation of higher Landau levels is pointed out.