Low-energy properties of the Kondo lattice model.

We study the zero-temperature properties of the Kondo lattice model within the dynamical mean-field theory. As an impurity solver we use the numerical renormalization group. We present results for the paramagnetic case showing the anticipated heavy-fermion physics, including direct evidence for the appearance of a large Fermi surface for antiferromagnetic exchange interaction. Allowing for the formation of a Néel state, we observe at finite doping an antiferromagnetic metal below a critical exchange interaction, which shows a crossover from a local moment antiferromagnet with a small Fermi surface for weak exchange coupling to a heavy-fermion antiferromagnet with a large Fermi surface for increasing exchange. Including lattice degrees of freedom via an additional Holstein term we observe a significant suppression of the Kondo effect, leading to a strongly reduced low-energy scale. For too large electron-phonon coupling we find a complete collapse of the heavy Fermi liquid and the formation of polarons.