Fluctuation-induced first order phase transitions in type-1.5 superconductors in zero external field

TL;DR

This paper investigates how nonmonotonic vortex interactions in multiband type-1.5 superconductors can induce a first-order phase transition, contrasting with the second-order transition in single-component models.

Contribution

It demonstrates that vortex interactions in type-1.5 superconductors can lead to a first-order phase transition, a novel finding not observed in traditional type-1 or type-2 systems.

Findings

Vortex interactions in type-1.5 superconductors are nonmonotonic, combining attraction and repulsion.

The superconducting transition can be first-order due to vortex loop proliferation.

This behavior differs from the second-order transition in single-component models.

Abstract

In a single-component Ginzburg-Landau model which possesses thermodynamically stable vortex excitations, the zero-field superconducting phase transition is second order even when fluctuations are included. Beyond the mean-field approximation the transition is described in terms of proliferation of vortex loops. Here we determine the order of the superconducting transition in an effective 3D vortex-loop model for the recently proposed multiband type-1.5 superconductors. The vortex interaction is nonmonotonic, i.e., exponentially screened and attractive at large separations, and short-range repulsive. We show that the details of the vortex interaction, despite its short-range nature, can lead to very different properties of the superconducting transition than found in type-1 and type-2 systems. Namely, the type-1.5 regime with nonmonotonic intervortex interaction can have a first-order vortex-driven phase transition not found in the single-band case.