Spin and charge dynamics in a renormalized perturbation theory

Abstract

We calculate the spin and charge dynamical susceptibilities of a strongly correlatedimpurity model in a renormalized perturbation theory. The irreducible vertices for thequasiparticle scattering are deduced from the renormalized parameters, which have beencalculated by fitting the low-lying levels of a numerical renormalization group(NRG) calculation to those of an effective Anderson model. The susceptibilities areasymptotically exact in the low frequency limit and satisfy the Korringa–Shiba relation.By comparing the results with those calculated from a direct NRG calculation,we show that the renormalized perturbation theory (RPT) description gives avery good description of the spin dynamics for all values of the local interactionU, not only at low frequencies but over the whole relevant frequency range.In the presence of a magnetic field the approach can be generalized using field dependentrenormalized parameters to calculate the transverse and parallel spin dynamicsusceptibilities. The RPT gives accurate results for the spin dynamics over the wholefrequency range and for all values of the magnetic field.