Transition from Type-I to Type-II Superconducting Behaviour with Temperature observed by $\mu$SR and SANS

TL;DR

This study examines how Bi doping in lead causes a transition from type-I to type-II superconductivity with temperature, using $$SR and SANS techniques to observe the change in magnetic behavior.

Contribution

It demonstrates the temperature-dependent transition in superconducting type in Bi-doped lead, highlighting the role of the Ginzburg-Landau parameter crossing the critical value.

Findings

Pure lead exhibits type-I superconductivity.

High Bi doping results in type-II behavior with flux lattice formation.

Intermediate doping shows both behaviors depending on temperature.

Abstract

We investigate the superconducting behaviour of Bi doped Pb. Pure lead shows type-I behaviour entering an intermediate state in a magnetic field. High dopings of Bi ($>$3%) lead to type-II behaviour showing a mixed state, where the magnetic field penetrates the superconductor in the form of a flux lattice. At intermediate doping, the sample shows both type-I and type-II behaviour depending on the temperature. This arises because the Ginzburg-Landau parameter $\kappa$ passes through its critical value of $1/\sqrt{2}$ with temperature.