Investigations of positive muons in crystalline samples, performed using the longitudinal field-quenching technique, furnished strong evidence for the existence of a novel paramagnetic muon species with a small anisotropic hyperfine interaction. The signatures of the novel species were found in intrinsic, but not in doped, samples (for dopant concentrations of about 1016/cm3). The new species was not formed immediately, but resulted from a reaction in which normal muonium transformed into the novel species. The reaction rate constant at 10K was found to be about 106/s. The hyperfine coupling of the new paramagnetic muon species corresponded, after re-scaling, to that of a H center, VH, which had been attributed to H which was trapped in vacancies. The longitudinal field-quenching data were tentatively explained in terms of the trapping of normal muonium in vacancies that were created during the slowing-down of implanted muons close to the end of their range.

Evidence for a novel muon species in crystalline silicon M.Schefzik, R.Scheuermann, L.Schimmele, J.Schmidl, A.Seeger, D.Herlach, O.Kormann, J.Major, A.Röck: Solid State Communications, 1998, 107[8], 395-400