Niobium in clean limit: an intrinsic type-I superconductor

TL;DR

This paper demonstrates that pure niobium is an intrinsic type-I superconductor in the clean limit, with disorder causing a transition to type-II, based on advanced microscopic calculations and thermodynamic criteria.

Contribution

It provides a detailed microscopic analysis and thermodynamic criterion to classify niobium as a type-I superconductor in the clean limit, clarifying its fundamental nature.

Findings

Pure niobium is a type-I superconductor in the clean limit.

Disorder induces a transition from type-I to type-II superconductivity.

Thermodynamic criteria offer a more accurate classification than Ginzburg-Landau parameter.

Abstract

Niobium is one of the most researched superconductors, both theoretically and experimentally. It is enormously significant in all branches of superconducting applications, from powerful magnets to quantum computing. It is, therefore, imperative to understand its fundamental properties in great detail. Here we use the results of recent microscopic calculations of anisotropic electronic, phonon, and superconducting properties, and apply thermodynamic criterion for the type of superconductivity, more accurate and straightforward than a conventional Ginzburg-Landau parameter $\kappa$ - based delineation, to show that pure niobium is a type-I superconductor in the clean limit. However, disorder (impurities, defects, strain, stress) pushes it to become a type-II superconductor.