Impurity entanglement entropy and the Kondo screening cloud

The screening of an impurity spin by conduction electrons is associated with the formation of a large Kondo screening cloud, of size ξK. We study the quantum entanglement between a region of size r surrounding the impurity and the rest of the sample (of total size R) using density matrix renormalization group and analytic methods. The corresponding ‘impurity entanglement entropy’, Simp, is shown to be a universal scaling function of r/ξK and r/R. We calculate this universal function using Fermi liquid theory in the regime ξK ≪ r.