Influence of superconductivity on quantum diffusion of the positive muon in aluminium

We present low temperature studies of muon diffusion and trapping in normal and superconducting aluminium doped with 75 at.ppm Li. The trapping rate at the lithium impurities, and thus the deduced diffusion rate, increases far more rapidly with decreasing temperature in the superconducting state compared with the normal state. This establishes the importance of conduction electrons at the Fermi surface in limiting long-range quantum diffusion in a metal.