MANY-BODY BAND-STRUCTURE AND FERMI-SURFACE OF THE KONDO-LATTICE

We present a theory for the single-particle excitations and Fermi surf ace of the Kondo lattice. Thereby we construct an effective Hamiltonia n describing the creation and propagation of single particle-like char ge fluctuations on a ''resonating-valence-bond background'' of local s inglets. The theory may be viewed as a Fermionic version of linear spi n-wave theory and is of comparable simplicity so that the calculations for the strong-coupling limit can be performed analytically. We calcu late the single-particle spectral function for the ''pure'' Kondo latt ice as well as for several extended versions: with a Coulomb repulsion between conduction and f electrons, Coulomb repulsion between conduct ion electrons, and a ''breathing'' f orbital. In all cases we study th e evolution of the spectrum in going from the Kondo insulator to the h eavy electron metal. We compare our results to exact diagonalization o f small clusters and find remarkable agreement in nearly all cases stu died. In the metallic case the f electrons participate in the Fermi su rface volume even when they are replaced by localized Kondo spins and the number of bands, their dispersion and spectral character, and the nontrivial (i.e., nonrigid bandlike) doping dependence including a pro nounced transfer of spectral weight are reproduced at least semiquanti tatively by the theory. [S0163-1829(98)02236-X].