A THEOREM ON PARTICLE NUMBER AND DENSITY OF STATES IN KONDO PROBLEM

A theorem is derived for the Kondo model describing the interaction of conduction electrons with a localized magnetic impurity. The theorem states that the model preserves exact particle-hole symmetry. This implies that for fixed chemical potential the average particle number is unchanged as compared to the noninteracting case independent of temperature and applied magnetic field. The consequences of the symmetry property for the one particle density of states are also investigated. Finally the theorem proves to be a useful tool to check current approximate theories of the Kondo effect on their validity. © 1969 Springer-Verlag.