The Kondo Screening Cloud: What Can We Learn from Perturbation Theory?

We analyze the role that the distance scale ${\xi }_K{=v}_F/T_K$ plays in the single-impurity Kondo problem using renormalization-group-improved perturbation theory. We derive the scaling functions for the local spin susceptibility in various limiting cases. In particular, we demonstrate exactly that the nonoscillating part of it should be short range, i.e., vanish for distances $r\gg 1/k_F$, and show explicitly that the interior of the screening cloud does not exhibit weak coupling behavior.