Excitation spectra in periodic Anderson and Kondo lattices

The one-particle excitation spectra and the momentum distribution functions for the periodic Anderson and Kondo Lattices in one and two dimensions and their dependence on the electron density are studied by using the exact diagonalization method with twisted boundary conditions on clusters with six and eight unit cells. We find the following: in the insulating state there exist more low-energy excitations than expected for a non-interacting system with the mixing gap, and in the metallic state the heavy fermion band is formed by reconstructing the low-energy excitations in the insulating state upon doping of carriers but not by simply shifting the Fermi level. As a result, the momentum distribution function has two characteristic momenta.