Phase coherence of conduction electrons below the Kondo temperature

We have measured the phase decoherence rate tau(-1)(phi) of conduction electrons in disordered Ag wires implanted with 2 and 10 ppm Fe impurities, by means of the weak-localization magnetoresistance. The Kondo temperature of Fe in Ag, T-K approximate to 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(-1)(phi) from the Fe impurities is clearly visible over the temperature range 40 mK-10 K. Below T-K, tau(-1)(phi) falls rapidly until T/T-K approximate to 0.1, in agreement with recent theoretical calculations. At lower T tau(-1)(phi) deviates from theory with a flatter T-dependence. Understanding this anomalous dephasing for T/T-K < 0.1 may require theoretical models with larger spin and number of channels.