Type-1.5 Superconductors

TL;DR

This paper reports the discovery of a novel type-1.5 superconducting state in MgB2, characterized by unique vortex interactions and patterns due to the coexistence of type-1 and type-2 conditions in its two components.

Contribution

It introduces the concept of type-1.5 superconductivity with experimental visualization and numerical simulation of unconventional vortex patterns in MgB2.

Findings

Observation of vortex-vortex attraction at long distances

Visualization of stripe- and gossamer-like vortex patterns

Demonstration of a mixed type-1.5 superconducting state

Abstract

We demonstrate the existence of a novel superconducting state in high quality two-component MgB2 single crystalline superconductors where a unique combination of both type-1 (kappa_1 < 0.707) and type-2 (kappa_2 > 0.707) superconductor conditions is realized for the two components of the order parameter. This condition leads to a vortex-vortex interaction attractive at long distances and repulsive at short distances, which stabilizes unconventional stripe- and gossamer-like vortex patterns that we have visualized in this type-1.5 superconductor using Bitter decoration and also reproduced in numerical simulations.