Gap Formation in the Symmetric Periodic Anderson Model in Infinite Dimensions

抄録

We study the symmetric periodic Anderson model in infinite dimensions by the selfconsistent second order perturbation theory. After solving the selfconsistent equations for the Green's functions, we calculate dynamical charge- and spin susceptibilities and dynamical conductivity as well as thermodynamic quantities and resistivity. Dynamical conductivity is also calculated by another second order perturbation theory, the iterated perturbation theory. At T=0, density of states has a gap around the chemical potential. We also find that at T=0 a gap appears in dynamical response functions. The resistivity is found to obey an activation-type temperature dependence at low temperatures. The gaps in the spin- and charge excitation spectrum are found to be equal in magnitude, and also to be equal to the gap in the density of states. On the other hand, the gap in the dynamical conductivity is larger because it is a direct gap. We further study the temperature dependence of these quantities, and show how a gap evolves as the temperature decreases. Furthermore, we discuss relations to experimental results on the so-called Kondo insulators.