The different development of the anisotropic upper critical field in MgB2 by aluminum and carbon doping

TL;DR

This study investigates how aluminum and carbon doping differently influence the anisotropic upper critical field in MgB2, revealing distinct mechanisms affecting superconducting properties and scattering rates.

Contribution

It provides a comparative analysis of the effects of Al and C doping on Hc2 in MgB2, highlighting different underlying mechanisms such as intrinsic Fermi level shifts and extrinsic disorder effects.

Findings

Al doping shifts the Fermi level, affecting Hc2 intrinsically.

C doping increases Hc2 significantly due to disorder effects.

Different scattering rates explain the contrasting impacts of Al and C doping.

Abstract

The temperature dependence of the upper critical field, Hc2, for both field directions in partially substituted polycrystalline MgB2 was determined. Whereas the suppression of Tc is similar for aluminum and carbon substituted samples, Hc2 is affected by the substitution in profoundly different ways. In the case of Al substitution changes can tentatively be described by intrinsic effects (shift of the Fermi level). In the C substituted samples, Hc2 is increased drastically, and extrinsic effects (disorder) have to play a major role. The strong contrast between the two substitutions is discussed, taking into account three relevant scattering rates.