Correlations in a Band Insulator

Using DMFT we find a discontinuous band-to-Mott insulator transition upon an increase in the local Coulomb repulsion in a covalent band insulator [1,2], defined as a band insulator with partially filled local orbitals. The corresponding band gap is a hybridization gap arising from a particular pattern of hopping integrals. Similar characteristics apply to materials such as FeSi, FeSb$_{2}$ or CoTiSb [3], some of which exhibit temperature dependent magnetic and transport properties reminiscent of Kondo insulators. Both charge and spin gaps in the covalent band insulator shrink with increasing Coulomb repulsion. At moderate interaction strengths the gap renormalization is well described by a renormalization factor analogous to the quasiparticle weight in a Fermi liquid. \\[4pt] [1] M. Sentef, J. Kune\v{s}, P. Werner, and A.P. Kampf, Phys. Rev. B \textbf{80}, 155116 (2009) \\[0pt] [2] A.P. Kampf, M. Kollar, J. Kune\v{s}, M. Sentef, and D. Vollhardt, arXiv:0910.5126