Strong-coupling expansion for a Kondo-lattice model

We consider a single tight-binding band of electrons interacting with localized spin-{} magnetic moments at every lattice site. We assume that in zeroth order the system is well described by noninteracting Kondo singlets, and discuss an expansion in the electron-hopping matrix element. To second order, the bandwidth is renormalized by a factor of 2, and an effective interaction between the singlets results. We discuss the properties of the model as a function of band filling, Kondo coupling, and Hubbard electron-electron interaction. In particular, we find that the system could exhibit a charge-density-wave ground state or triplet superconductivity for certain ranges of parameters.