We study the effect of on-site Coulomb repulsion on the process of resonant tunneling. We find that the tunneling peak results from a crossover from the high-temperature Kondo phase to the low-temperature mixed-valence phase of the system when the chemical potential is varied across the on-site localized-state energy. Consequently, the line shape is non-Lorentzian, with rather unusual temperature dependence. Moreover, a magnetic field does not split the tunneling peak, but the line shape is modified. The effect of coupling between localized states is also discussed.

• Received 9 May 1988

DOI:https://doi.org/10.1103/PhysRevLett.61.1768