The importance of thermal disorder and electronic occupation for the T-dependence of the optical conductivity in FeSi and MnSi

TL;DR

This study investigates how thermal disorder and electronic occupation influence the temperature dependence of optical conductivity in FeSi and MnSi, revealing contrasting effects and aligning with experimental observations.

Contribution

It demonstrates that structural disorder and electronic Fermi-Dirac distribution have opposing effects on spectral weight temperature dependence in FeSi and MnSi.

Findings

Spectral weight increases with temperature in FeSi.

Spectral weight decreases with temperature in MnSi.

Magnetic moment variation in MnSi has minor impact.

Abstract

The spectral weight (SW) for optical transitions in FeSi and MnSi are calculated as function of temperature by means of LMTO-LDA band calculations. The main effects, caused by structural disorder and electronic Fermi-Dirac distribution, act oppositely on the T-dependence of the SW, while the variation of the magnetic moment in MnSi has only a minor effect. The calculations agree with the experimental findings of an increasing SW in FeSi and a decreasing SW in MnSi as function of T. The results can be understood from the change of the bandstructure with disorder.