Local tunneling and metastability of muonium in CuCl.

Measurements of the muon spin relaxation of muonium show that the Mu I center in CuCl is an example of metastability in which isolated muonium tunnels locally around the tetrahedral interstitial site with four Cu nearest neighbors, with the stable corm (Mu II ) quasistationary at the same interstitial. For T<30K the inverse correlation time 'associated with the damped tunneling motion increases with decreasing temperature according to a power law T -2.7(I) which is close to that observed previously for long-range quantum diffusion of muonium in insulators