Muon motion in pure and weakly doped aluminium

We have studied the diffusion and localization of positive muons in pure and weakly doped aluminium, in the temperature range 30 mK-100 K, by measuring the damping parameter of muon spin rotation (μSR) signal. In this paper we discuss some of our recent results and draw the following conclusion: i) in pure Al, positive muons are delocalized in band states (coherent motion); ii) in Al doped with 5-70 ppm Mn, the temperature, concentration and field dependences of the damping parameter suggest diffusion or capture limited trapping to octahedral interstitial site in the aluminium lattice below 1 K; iii) above 2 K a two-state diffusion-trapping model explains well the peak in the damping parameter, which appears at 15-50 K for the dopants Mn, Mg, Li and Ag so far studied. (orig.)