Theory of tunneling centers in metallic systems: Role of excited states and orbital Kondo effect

The interaction between a tunneling atom in a double potential well and the conduction electrons of different angular momenta results in an anisotropic two-channel orbital Kondo problem, but the Kondo temperature ${\mathit{T}}_{\mathit{K}}$ found earlier has always been somewhat small. That difficulty can be resolved by including some of the excited states of the atom in the well. The ${\mathit{T}}_{\mathit{K}}$ calculated is around 1–10 K in agreement with experiments. The same result can be obtained even if the direct electron assisted tunneling is ignored.