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 + 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 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.