Inelastic scattering from quantum impurities

We review the non-perturbative theoretical framework set up recently to compute the inelastic scattering cross section from quantum impurities [G. Zar\'and {\it et al.}, Phys. Rev. Lett. {\bf 93}, 107204 (2004)] and show how it can be applied to a number of quantum impurity models. We first use this method for the $S=1/2$ single-channel Kondo model and the Anderson model. In both cases, a large plateau is found in the inelastic scattering rate for incoming energies above $T_K$, and a quasi-linear regime appears in the energy range $0.05 T_K < \omega < 0.5 T_K$, in agreement with the experimental observations. We also present results for the 2-channel Kondo model, the prototype of all non-Fermi liquid models, and show that there half of the scattering remains inelastic even at the Fermi energy.