ABSTRACT
This chapter discusses recent studies on both quantum diffusion and electron transport in condensed matter using muon spin research (μSR) techniques paying particular attention to processes of particle localisation and delocalization. It deals with the mass and charge transport, i.e. dynamics of neutral particles and charged particles, limited by potential barriers. Because of the unique mass of the muon one can hardly mention any other example where quantum diffusion was observed in such a wide temperature range as for both µ+ and Mu. The other reason for the success of the quantum diffusion study using muons is the sensitivity of the muon spin relaxation (µSR) and muonium spin relaxation techniques to µ+ and Mu dynamics. An understanding of the possible mechanisms of particle localisation and delocalisation in crystals due to interactions with crystalline defects and lattice excitations is very important in the context of quantum diffusion phenomena.
