By measuring the muon spin relaxation rate of muonium as it moved from site to site in a host lattice with nuclear spins, it was possible to derive an average correlation time, τ, for fluctuations in the nuclear hyperfine field which acted upon the unpaired electron. Provided that the motion was incoherent (diffusive), τ was inversely proportional to the diffusion constant. Such measurements were reported here for isotropic muonium at temperatures ranging from 20mK to 300K. Large differences were found in the muonium motion, and were most marked at low temperature; where l/τ became temperature-independent below about 10K in GaAs. A study was also made of the diffusive behavior of muonium in various GaAs samples in order to detect the possible effect of slight crystalline imperfections.

W.Schneider, R.F.Kiefl, E.J.Ansaldo, J.H.Brewer, K.Chow, S.F.J.Cox, S.A.Dodds, R.C.Duvarney, T.L.Estle, E.E.Haller, R.Kadono, S.R.Kreitzman, R.L.Lichti, C.Niedermayer, T.Pfiz, T.M.Riseman, C.Schwab: Materials Science Forum, 1992, 83-87, 569-74