Antivortices due to competing orbital and paramagnetic pair-breaking effects

TL;DR

This paper predicts stable vortex-antivortex structures in a quasi-two-dimensional superconductor under a tilted magnetic field, highlighting the interplay of orbital and paramagnetic effects near the critical field.

Contribution

It introduces the existence of stable vortex-antivortex states in a superconductor with combined orbital and spin pair-breaking effects, expanding understanding of vortex matter.

Findings

Stable vortex-antivortex states exist near zero tilt angle.

Spectrum interpolates between vortex and FFLO states.

Results align with recent mesoscopic antivortex predictions.

Abstract

Thermodynamically stable vortex-antivortex structures in a quasi-two-dimensional superconductor in a tilted magnetic field are predicted. For this geometry, both orbital and spin pair-breaking effects exist, with their relative strength depending on the tilt angle \Theta. The spectrum of possible states contains as limits the ordinary vortex state (for large \Theta) and the Fulde-Ferrell-Larkin-Ovchinnikov state (for \Theta=0). The quasiclassical equations are solved near H_{c2} for arbitrary \Theta and it is shown that stable states with coexisting vortices and antivortices exist in a small interval close to \Theta=0. The results are compared with recent predictions of antivortices in mesoscopic samples.