Shallow-band superconductors: pushing superconductivity types apart

TL;DR

This paper explores how multi-band superconductors with a shallow band often do not fit into the traditional type I or type II categories, exhibiting unconventional mixed states.

Contribution

It reveals that such superconductors frequently occupy an inter-type region, challenging the conventional classification of superconductivity types.

Findings

Shallow-band multi-band superconductors often fall into the inter-type interval.

These systems display unconventional mixed state configurations.

They challenge the traditional dichotomy of superconductivity types.

Abstract

Magnetic response is a fundamental property of superconducting materials, which helps to distinguish two superconductivity types: the ideally diamagnetic type I and type II, which can develop the mixed state with Abrikosov vortices. We demonstrate that multi-band superconductors with one shallow band, that have recently attracted much attention for their high critical temperatures and unusual properties, often stay apart of this simple classification. In a wide range of microscopic parameters such systems fall into the inter-type or transitional interval in between the standard types and display unconventional mixed state configurations.