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 $T_K$ is computed as a function of barrier parameters. We find that for special parameters $T_K$ can be close to 1 K and it can be of the same order of magnitude as the renormalized splitting $\Delta .$ However, in the perturbative regime we always find that $T_K\lesssim \Delta$ with $T_K\lesssim 1\mathrm{K}$ [I. L. Aleiner et al., Phys. Rev. Lett. 86, 2629 (2001)]. We also find that $\Delta$ remains unrenormalized at energies above the Debye frequency, ${\omega }_{\mathrm{Debye}}.$