Thermal and Dynamical Properties of the Two-band Hubbard Model Compared with FeSi

TL;DR

This paper investigates the thermal and dynamical properties of a two-band Hubbard model as a representation of FeSi, revealing that electron correlations have limited impact on the energy gap and that the optical gap fills at low temperatures, aligning with experimental observations.

Contribution

The study applies self-consistent second-order perturbation theory with local approximation to analyze the model, providing new insights into correlation effects on FeSi's properties.

Findings

Correlation effects do not significantly reduce the energy gap.

Optical conductivity gap fills at lower temperatures than the gap size.

Results are consistent with experimental data on FeSi.

Abstract

We study the two-band Hubbard model introduced by Fu and Doniach as a model for FeSi which is suggested to be a Kondo insulator. Using the self-consistent second-order perturbation theory combined with the local approximation which becomes exact in the limit of infinite dimensions, we calculate the specific heat, the spin susceptibility and the dynamical conductivity and point out that the reduction of the energy gap due to correlation is not significant in contrast to the previous calculation. It is also demonstrated that the gap at low temperatures in the optical conductivity is filled up at a rather low temperature than the gap size, which is consistent with the experiment.