Dephasing in Metals by Two-Level Systems in the 2-Channel Kondo Regime

We point out a novel, nonuniversal contribution to the dephasing rate $1/{\tau }_{\varphi }\equiv {\gamma }_{\varphi }$ of conduction electrons in metallic systems: scattering off nonmagnetic two-level systems (TLSs) having almost degenerate Kondo ground states. In the regime ${\Delta }_{\mathrm{ren}}<T<\mathrm{}{T}_K$ ( ${\Delta }_{\mathrm{ren}}=\mathrm{renormalized}\mathrm{level}\mathrm{splitting}$, $T_K=\mathrm{Kondo}\mathrm{temperature}$), such TLSs exhibit non-Fermi-liquid physics that can cause ${\gamma }_{\varphi }$, which generally decreases with decreasing $T$, to seemingly saturate in a limited temperature range before vanishing for $T\to 0$. This could explain the saturation of dephasing recently observed in gold wires [Mohanty et al., Phys. Rev. Lett. 78, 3366 (1997)].