The K ondo Effect

Abstract A review is presented of the Kondo effect, with a summary of key experiments and theoretical treatments. Hamiltonians surveyed, in addition to the single‐impurity spin‐1/2 Kondo model, are multichannel Kondo models, the Coqblin–Schrieffer model, two‐impurity problems, including two‐channel, two‐impurity, the Anderson model, and a brief summary of the Kondo lattice. Exact, known results are a focus. Non‐Fermi‐liquid fixed points are a feature of more than one Kondo Hamiltonian, and the phases of these systems can be unusual and quite interesting. Techniques surveyed include scaling, numerical renormalization group, 1/ N expansion, Bethe ansatz, and conformal field theory. We conclude with a review of the scanning tunneling microscope experiments on Kondo systems, one of the best current realizations of few‐impurity Kondo models, and a source of often surprising new physics.