Phase coherence of conduction electrons below the Kondo temperature

Abstract

We have measured the phase decoherence rate, $\tau_{\phi}^{-1}$ of conduction electrons in disordered Ag wires implanted with 2 and 10 parts per million Fe impurities, by means of the weak localization magnetoresistance. The Kondo temperature of Fe in Ag, $T_K \approx 4$ K, is in the ideal temperature range to study the progressive screening of the Fe spins as the temperature $T$ falls below $T_K$. The contribution to $\tau_{\phi}^{-1}$ from the Fe impurities is clearly visible over the temperature range 40 mK -- 10 K. Below $T_K$, $\tau_{\phi}^{-1}$ falls rapidly until $T/T_K \approx 0.1$, in agreement with recent theoretical calculations. At lower $T$, $\tau_{\phi}^{-1}$ deviates from theory with a flatter $T$-dependence. We speculate that this latter behavior is due to incomplete screening of the s=2 Fe impurities by the conduction electrons.