Dynamic Spin Correlation Function near the Antiferromagnetic Quantum Phase Transition of Heavy-Fermions

Abstract

The dynamical spin susceptibility is studied in the magnetically-disordered phase of heavy-Fermion systems near the antiferromagnetic quantum phase transition. In the framework of the $S=1/2$ Kondo lattice model, we introduce a perturbative expansion treating the spin and Kondo-like degrees of freedom on an equal footing. The dynamical spin susceptibility displays a two-component behaviour in agreement with the inelastic neutron scattering (INS) experiments performed in $CeCu_{6}$, $Ce_{1-x}La_{x}Ru_{2}Si_{2}$ and $UPt_{3}$: a quasielastic q-independent peak as in a Fermi liquid theory, and a strongly q-dependent inelastic peak typical of a non-Fermi liquid behaviour. Very strikingly, the position of the inelastic peak is found to be pushed to zero at the antiferromagnetic transition. The picture is consistent with the neutron cross sections observed in INS experiments.