Type-1.5 superconductivity in multicomponent systems

TL;DR

This paper discusses the emergence of type-1.5 superconductivity in multicomponent systems, characterized by multiple coherence lengths, leading to unique vortex behaviors and physical phenomena near phase transitions between different symmetry states.

Contribution

It introduces the concept of type-1.5 superconductivity arising from multicomponent systems and analyzes its physical consequences near symmetry-breaking phase transitions.

Findings

Existence of multiple coherence lengths in multiband superconductors.

Vortex attraction at long range and repulsion at short range in type-1.5 regime.

Vortex clustering and phase separation phenomena.

Abstract

In general a superconducting state breaks multiple symmetries and, therefore, is characterized by several different coherence lengths $\xi_i$, $i=1,...,N$. Moreover in multiband material even superconducting states that break only a single symmetry are nonetheless described, under certain conditions by multi-component theories with multiple coherence lengths. As a result of that there can appear a state where some coherence lengths are larger and some are smaller than the magnetic field penetration length $\lambda$: $\xi_1\leq \xi_2... < \sqrt{2}\lambda<\xi_M\leq...\xi_N$. That state was recently termed "type-1.5" superconductivity. This breakdown of type-1/type-2 dichotomy is rather generic near a phase transition between superconducting states with different symmetries. The examples include the transitions between $U(1)$ and $U(1)\times U(1)$ states or between $U(1)$ and $U(1)\times Z_2$ states. The later example is realized in systems that feature transition between s-wave and $s+is$ states. The extra fundamental length scales have many physical consequences. In particular in these regimes vortices can attract one another at long range but repel at shorter ranges. Such a system can form vortex clusters in low magnetic fields. The vortex clustering in the type-1.5 regime gives rise to many physical effects, ranging from macroscopic phase separation in domains of different broken symmetries, to unusual transport properties.