Metal-insulator transition and magnetism in correlated band insulator: FeSi and Fe$_{1-x}$Co$_{x}$Si

TL;DR

This study uses LDA+DMFT calculations to analyze the spectral and magnetic properties of FeSi and Fe$_{1-x}$Co$_{x}$Si, confirming a correlated band insulator scenario and explaining magnetic transitions and doping effects.

Contribution

It demonstrates that a correlated band insulator model aligns with experimental data for FeSi and explains magnetic and doping phenomena using LDA+DMFT.

Findings

Coulomb correlations cause band narrowing and mass renormalization near the Fermi level.

Temperature-dependent spectral functions reproduce the transition from nonmagnetic semiconductor to metal.

Cobalt doping induces itinerant ferromagnetism accurately described by LDA+DMFT.

Abstract

The LDA+DMFT (local density approximation combined with dynamical mean-field theory) computation scheme has been used to study spectral and magnetic properties of FeSi and Fe$_{1-x}$Co$_{x}$Si. Having compared different models we conclude that a correlated band insulator scenario in contrast to Kondo insulator model agrees with FeSi band structure as well as experimental data. Coulomb correlation effects lead to band narrowing of the states near the Fermi level with mass renormalization parameter $m^*\approx 2$ in agreement with the results of angle-resolved photoemission spectroscopy (ARPES). Temperature dependence of spectral functions and magnetic susceptibility calculated in DMFT reproduces transition from nonmagnetic semiconductor to metal with local magnetic moments observed experimentally. Cobalt doping leads to ferromagnetism that has itinerant nature and can be successfully described by LDA+DMFT method.