Fermi surface of the one-dimensional Kondo-lattice model

We show a strong indication of the existence of a large Fermi surface in the one-dimensional Kondo-lattice model. The characteristic wave vector of the model is found to be (Formula presented)=(1+ρ)π/2, ρ being the density of the conduction electrons. This result is at first obtained for a variant of the model that includes an antiferromagnetic Heisenberg interaction (Formula presented) between the local moments. It is then directly observed in the conventional Kondo lattice ((Formula presented)=0), in the narrow range of Kondo couplings where the long distance properties of the model are numerically accessible.