Coherent Propagation and Strain-Induced Localization of Muons in Al

Positive muons implanted in single-crystal Al doped with Mn are localized below 20 K in contrast to the case of pure Al, where the muon is completely delocalized down to 1 K. Applying the Anderson theory of localization, we show consistently that a coherent tunneling state, which exists in pure Al, is destroyed under the influence of lattice strains generated by the Mn impurities. Our data suggest strongly that the muons are localized at tetrahedral sites at 15 K.