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 k(F)=(1 + rho)pi/2, rho 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 J(H) between the local moments. It is then directly observed in the conventional Kondo lattice (J(H)=0), in the narrow range of Kondo couplings where the long distance properties of the model are numerically accessible.