Low-Temperature Behavior of a Tunneling Atom Interacting with a Degenerate Electron Gas

A renormalization-group analysis of a tunneling atom interacting with a degenerate electron gas is presented. We consider both electronic screening and electron-assisted tunneling. In the case where the latter is strong, it is shown that, because of the spin degeneracy, the low-temperature behavior is dominated by the nontrivial fixed point of the multichannel Kondo model.