This study explored the dynamic behavior of hydrogen in diamond, via a study of the hydrogenic analogue species known as the neutral atomic muonium state (MuT ≡ μ+e-). This could be readily studied by the transverse (longitudinal) field muon spin rotation (relaxation) techniques, briefly known as TF-μSR or LF-μSR respectively. This work focuses on the TF-μSR results for the paramagnetic MuT state. The MuT forms when an implanted positive muon captures an electron in crystalline solid-state materials. It occupies the tetrahedral interstitial site and diffuses via a pathway of these sites. The small mass of MuT was intermediate between the light electron and the heavy hydrogen, and was therefore suitable for studies of quantum diffusion in crystalline materials. In the process of diffusion, the spin polarization of the muon ensemble would be affected by interaction with electrons, via formation of correlated states or with the environment via dissipative processes. Such interactions could be monitored, almost background free and very precisely, in a host of experimental modes. This allows a powerful spectroscopy of the formed states as well as the monitoring of the dynamics of those states. In this work, the observables for both the MuT (73%) and μd+ (4.3%) states were measured in the 13C sample at temperatures ranging from 11mK to 320K, at an applied field of 5mT. The measured spin relaxation rate for the MuT in the 13C sample was interpreted within the framework of quantum diffusion. The data showed that quantum diffusion of the MuT state occurred up to unusually high temperatures in diamond. No evidence of diffusion could be obtained for the diamagnetic state.

Quantum Diffusion of Isotropic Muonium, Mut, in a 13C Diamond. Machi, I.Z., Connell, S.H., Dalton, M., Sithole, M.J., Bharuth-Ram, K., Cox, S.F.J., Baines, C.: Diamond and Related Materials, 2004, 13[4-8], 909-13