Transverse field muon spin rotation measurements on diamonds with deliberately prepared defects showed strong temperature dependence of the spin relaxation rate of the tetrahedral interstitial muonium species, MuT. These results were explained by considering coherent tunnelling, below 300K, followed by deep trapping at the defects. These results provided the first evidence for quantum diffusion of neutral MuT in diamond.

Quantum Diffusion of Tetrahedral Interstitial Muonium in Diamond. Machi, I.Z., Connell, S.H., Sellschop, J.P.F., Bharuth-Ram, K., Doyle, B.P., Maclear, R.D., Major, J., Scheuermann, R.: Physica B, 2000, 289-290, 468-72