Thermal conductivity of Al-doped MgB2: Impurity scattering and the validity of the Wiedemann-Franz law

TL;DR

This study investigates how aluminum doping affects the thermal conductivity of MgB2, revealing impurity-induced scattering effects and confirming the Wiedemann-Franz law's applicability in doped and pure samples.

Contribution

It provides detailed measurements of thermal conductivity in Al-doped MgB2 and demonstrates that Al impurities enhance intraband scattering in both electronic bands, challenging previous assumptions.

Findings

Al doping reduces electronic heat transport

Impurities increase intraband scattering in both bands

Wiedemann-Franz law remains valid in doped MgB2

Abstract

We report data on the thermal conductivity K(T,H) along the basal plane of the hexagonal crystal structure of superconducting Mg{1-y}Al{y}B2 with y=0.02 and 0.07 at temperatures between 0.5 and 50 K and in external magnetic fields between 0 and 70 kOe. The substitution of Al for Mg leads to a substantial reduction of the heat transport via electronic quasiparticles. The analysis of the K(T,H) data implies that the Al impurities provoke an enhancement of the intraband scattering rate, almost equal in magnitude for both the sigma- and the pi band of electronic excitations. This is in contrast with conclusions drawn from analogous data sets for material in which carbon replaces boron and where mainly the intraband scattering rate of the sigma band is enhanced. Our complete data set, including additional results of measurements of the low-temperature thermal conductivity of pure MgB2, confirms the validity of the Wiedemann-Franz law for both pure and doped MgB2.