Calculation of Optical Conductivity, Resistivity and Thermopower of Filled Skutterudite CeRu${}_4$Sb${}_{12}$ based on a Realistic Tight-binding Model with Strong Correlation

The filled-skutterudite compound CeRu${}_4$Sb${}_{12}$ shows a pseudo-gap structure in the optical conductivity spectra similar to the Kondo insulators, but metallic behavior below 80 K. The resistivity shows a large peak at 80 K, and the Seebeck coefficient is positive and also shows a large peak at nearly the same temperature. In order to explain all these features, a simplified tight-binding model, which captures the essential features of the band calculation, is proposed. Using this model and introducing the correlation effect within the framework of the dynamical mean field approximation and the iterative perturbation theory, the temperature dependences of the optical conductivity, resistivity and the Seebeck coefficient are calculated, which can explain the experiments.