Dephasing in metals by two-level systems in the 2-channel Kondo regime

We point out a novel, nonuniversal contribution to the dephasing rate 1/tau (phi) = gamma(phi) of conduction electrons in metallic systems: scattering off nonmagnetic two-level systems (TLSs) having almost degenerate Kondo gro und states. In the regime Delta(ren) < T < T-K (Delta(ren) = renormalized l evel splitting, T-K = Kondo temperature), such TLSs exhibit non-Fermi-liqui d physics that can cause gamma(phi) which generally decreases with decreasi ng T, to seemingly saturate in a limited temperature range before vanishing for T --> 0. This could explain the saturation of dephasing recently obser ved in gold wires [Mohanty et at, Phys. Rev. Lett. 78, 3366 (1997)].