Excitation Gap in the Kondo Insulator with Coulomb Interaction between Conduction Electrons

We have investigated the effects of the Coulomb interaction between conduction electrons on the excitation gap of the Kondo insulator. As a theoretical model of the Kondo insulator, the periodic Anderson model (PAM) has been used under particle–hole symmetry. We have treated the PAM with the Coulomb interaction between the conduction electrons, denoted by Uc, using the dynamic mean-field theory (DMFT) with the iterated perturbation theory as the DMFT impurity solver. With increasing Uc, the gap of the density of states at absolute zero widens and the characteristic temperature at which the electronic state begins to be reconstructed increases. We have found, via the perturbative approach, that the gap in the theoretical model of the Kondo insulator is widened by Uc, at least in the weak-coupling regime.