Electronic structure calculations were performed for muonium. These indicated a transfer matrix element, |t(o)|, of about 0.009K and a muonium-phonon coupling strength that was characterized by a deformation potential of about 2.6eV. When incorporated into the small-polaron quantum diffusion model, these values predicted a cross-over from coherent to incoherent tunnelling at about 100K; as observed in other alkali halides. However, a large upward renormalization of |t(o)| would be required before the theory could reproduce the observed tunnelling rates.

T.McMullen, J.Meng, J.M.Vail, P.Jena: Physical Review B, 1995, 51[22], 15879-84