Local density of states in the vicinity of a Kondo hole

Abstract

The substitution of magnetic ions by nonmagnetic impurities in a Kondo lattice gradually destroys the coherence of the heavy fermion groundstate. These nonmagnetic impurities are frequently referred to as Kondo holes. We consider a simple cubic Anderson lattice without orbital degeneracy and study the effects of the scattering off the Kondo hole in the local density of f states in the neighborhood of the nonmagnetic impurity. The correlations within the f band are introduced via a self-energy, evaluated to second order perturbation in U. We use the 1/d expansion method of Schweitzer and Czycholl to leading order (d=∞) in which the k integrations are properly carried out, but the k dependence of the self-energy is neglected. For a Kondo insulator we find a δ-function-like boundstate in the gap. The spectral weight of the boundstate decreases rapidly with increasing distance from the impurity. In the metallic case we obtain a resonance of finite width in the pseudogap of the lattice, which again is localized in the neighborhood of the Kondo hole. These states only appear in the coherent phase and disappear in the continuum at higher temperatures.