A SIMPLE THEORY OF THE KONDO HOLE

The Kondo hole is an isolated nonmagnetic impurity in a heavy-fermion lattice. Experimentally, the Kondo hole can be realized by La or Th atoms replacing a Ce ion in a stoichiometric Ce compound or by Th impurities in a U-heavy-fermion system. Adding impurities to a Kondo lattice gradually destroys the coherence of the heavy-fermion ground state. Perturbations of the coherent state are conveniently studied in the f-electron density of states. We consider a dispersionless orbitally nondegenerate f band locally hybridized with one nearest-neighbor hopping tight-binding conduction band on a simple cubic lattice. A hybridization gap opens in the symmetric case, and the Kondo hole introduces a bound state in the gap. We study the effects of the scattering on the local density of f states in the neighborhood of the nonmagnetic impurity. The effects of the correlations within the f band are introduced via a self-energy, evaluated to second-order perturbation in U, using the d = infinity treatment of Schweitzer and Czycholl [Solid State Commun. 74, 735 (1990)].