GENERALIZED HAMILTONIAN FOR TUNNELING CENTERS IN METALLIC SYSTEMS

The electron assisted hopping rate of an atom is calculated for an assymmetric double well potential. It is shown that the intuitive results of Vladar and Zawadowski based on barrier fluctuation agree with the matrix elements obtained by direct evaluation of the electron scattering amplitude due to the atom. However, the assisted hopping rate can not be interpreted as a simple consequence of the change in the Gamow factor but the prefactor is also affected due to potential fluctuations. Carrying out a one-dimensional calculation we show that the assisted hopping to higher energy levels may be quite large. This might strongly influence the evolution of the effective coupling constants and thus the characteristic temperature of the orbital Kondo effect.