Schwinger Boson approach to the fully screened Kondo model
  We apply the Schwinger boson scheme to the fully screened Kondo model and generalize the method to include antiferromagnetic interactions between ions. Our approach captures the Kondo crossover from local moment behavior to a Fermi liquid with a non-trivial Wilson ratio. When applied to the two impurity model, the mean-field theory describes the "Varma Jones" quantum phase transition between a valence bond state and a heavy Fermi liquid. 
J. Rech, P. Coleman, G. Zarand, O. Parcollet