Temperature-dependent correlations in covalent insulators: Dynamical mean-field approximation

Motivated by the peculiar behavior of FeSi and FeSb(2), 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 nonmagnetic insulator to high-temperature paramagnetic metal with parameters realistic for FeSi and FeSb(2) 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.