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

We point out a novel, non-universal contribution to the dephasing rate $1/\tau_\phi \equiv \gamma_\phi$ of conduction electrons in metallic systems: scattering off non-magnetic two-level systems (TLSs) having almost degenerate Kondo ground states. In the regime $\Delta_{ren} < T < T_K$ ($\Delta_{ren}$ = renormalized level splitting, $T_K$ = Kondo temperature), such TLSs exhibit non-Fermi-liquid physics that can cause $\gamma_\phi$, 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)].