Orbital Kondo behavior from dynamical structural defects

The interaction between an atom moving in a model double-well potential and the conduction electrons is treated using renormalization-group methods in next-to-leading logarithmic order. A large number of excited states is taken into account and the Kondo temperature TK is computed as a function of barrier parameters. We find that for special parameters TK can be close to 1 K and it can be of the same order of magnitude as the renormalized splitting D. However, in the perturbative regime we always find thatTK&D with TK& 1K @I. L. Aleiner et al., Phys. Rev. Lett. 86, 2629 ~2001!#. We also find thatD remains unrenormalized at energies above the Debye frequency, v Debye .