SPECTRAL WEIGHT AND BAND FILLING IN THE KONDO-LATTICE

The Kondo lattice has been investigated in the case that the Kondo exc hange dominates the kinetic energy and for vanishing exchange between localized spins. Without kinetic energy, the problem can be solved exa ctly, leading to local singlet states. The kinetic energy leads to a b roadening of these states into a band which has been calculated by pro jecting the hopping term onto the singlet states. The statistics of th e singlet states is completely different from the usual free fermion c ase, leading to a reduced spectral weight of that band by a factor bet ween four (for small filling of the singlet band) and two (for large f illing). The changed spectral weight also leads to a different filling of the singlet band in comparison with free fermions. (C) 1998 Elsevi er Science B.V.