The loss of anisotropy in MgB2 with Sc substitution and its relationship with the critical temperature

TL;DR

This study investigates how scandium substitution in MgB2 reduces electrical anisotropy and correlates this change with the decrease in critical temperature, highlighting the importance of sigma-band anisotropy for high Tc superconductivity.

Contribution

It provides a computational analysis linking anisotropy loss with Tc reduction in (Mg,Sc)B2, and compares it with other doped systems, emphasizing the role of sigma-band anisotropy.

Findings

Anisotropy drops with less than 30% Sc content.

Anisotropy reduction coincides with lower Tc and diminished Kohn anomaly.

Similar anisotropy loss observed in Al and C doped MgB2.

Abstract

The electrical conductivity anisotropy of the sigma-bands is calculated for the (Mg,Sc)B2 system using a virtual crystal model. Our results reveal that anisotropy drops with relatively little scandium content (< 30%); this behaviour coincides with the lowering of Tc and the reduction of the Kohn anomaly. This anisotropy loss is also found in the Al and C doped systems. In this work it is argued that the anisotropy, or 2D character, of the sigma-bands is an important parameter for the understanding of the high Tc found in MgB2.