Temperature dependent correlations in covalent insulators

TL;DR

This study explores how local electronic correlations influence the magnetic, transport, and optical properties of covalent insulators, revealing a temperature-driven crossover from insulator to metal in models relevant to FeSi and FeSb2.

Contribution

It demonstrates that the behavior of FeSi is due to generic properties of covalent insulators, not solely Kondo insulator physics, using a dynamical mean-field approach.

Findings

Crossover from non-magnetic insulator to paramagnetic metal with temperature.

Behavior of FeSi is explained by generic covalent insulator properties.

Results challenge the Kondo insulator interpretation for FeSi.

Abstract

Motivated by the peculiar behavior of FeSi and FeSb2 we study the effect of local electronic correlations on magnetic, transport and optical properties in a specific type of band insulator, namely a covalent insulator. Investigating a minimum model of covalent insulator within a single-site dynamical mean-field approximation we are able to obtain the crossover from low temperature non-magnetic insulator to high-temperature paramagnetic metal with parameters realistic for FeSi and FeSb2 systems. Our results show that the behavior of FeSi does not imply microscopic description in terms of Kondo insulator (periodic Anderson model) as can be often found in the literature, but in fact reflects generic properties of a broader class of materials.