Critical Field of MGB2 : Crossover from Clean to Dirty Regimes

TL;DR

This study investigates how disorder affects the upper critical field in MgB2, revealing a crossover from clean to dirty regimes and explaining anomalous doping effects.

Contribution

It introduces a controlled method to vary disorder in MgB2 and analyzes the crossover between clean and dirty regimes in different electronic bands.

Findings

Clean regime persists when p bands are dirty.

s bands are midway between clean and dirty.

Al doping causes Bc2 to decrease with increased doping.

Abstract

We have studied the upper critical field, Bc2, in poly-crystalline MgB2 samples in which disorder was varied in a controlled way to carry selectively p and s bands from clean to dirty limit. We have found that the clean regime survives when p bands are dirty and s bands are midway between clean and dirty. In this framework we can explain the anomalous behaviour of Al doped samples, in which Bc2 decreases as doping increases.