Density of states for the asymmetric Anderson model

The Anderson model is studied using a procedure of Green’s function decoupling, as a function of the parameters U (intra-atomic Coulomb interaction), E0-EF (position of the d-level compared to the Fermi level), Δ (width of the virtual d-level), and the temperature T. In the case of a Kondo impurity, i.e., U→∞ and ‖E0-EF‖≫Δ, the density of states consists in three peaks: the two resonances at E0 and E0+U and a very narrow peak around the Fermi level. We discuss the temperature dependence of the density of states using the approximate Green’s functions: the peak at the Fermi level has a width of the order of the Kondo temperature TK at T = 0 K and it disappears gradually at higher temperature. In the case of a mixed valence impurity we show, using the same decoupling procedure, that the peak at the Fermi level disappears when ‖E0-EF‖ becomes of the order of Δ.