Abstract
The diffusion of positive muons (≊0.11×proton mass) in copper was studied experimentally by the zero-field muon-spin-relaxation method in a temperature (T) range from 70 mK to 190 K, using a pulsed muon beam suitable for the present method. The measurements were performed in three copper samples of different purities to see the effect of impurities on the nature of the diffusion. We find that the diffusion (hopping) rate ν in ultrapure copper decreases rapidly with decreasing temperature, reaches a minimum at T=30–70 K, then begins to increase. The T dependence in the low-temperature region follows (α≃0.67±0.03) at 0.5–10 K and levels off below 0.5 K. The behavior is strongly modified by impurity consisting of ≊100 ppm iron below 10 K. The T dependence in the pure copper is accounted for by new theories developed independently by Kondo and by Yamada, predicting a hopping rate ν∝(0≤K≤1/2 for a single charged particle), where the factor comes from the renormalization of the muon tunneling matrix due to the nonadiabaticity of the conduction electron interacting with the moving muon. From the present results the constant K is determined to be K=0.16±0.01.
- Received 6 July 1988
DOI:https://doi.org/10.1103/PhysRevB.39.23
©1989 American Physical Society