Nuclear hyperfine structure of muonium in CuCl resolved by means of avoided level crossing

We report detailed avoided-level-crossing spectra of a muonium center (${\mathrm{Mu}}^{\mathrm{II}}$) in single-crystal CuCl in a magnetic field range of 4–5 T and at a temperature of 100 K. The hyperfine parameters of the muon and the closest two shells of nuclei indicate that this center consists of muonium at a tetrahedral interstice with four Cu nearest neighbors and six Cl next-nearest neighbors and that the spin density is appreciable on the muon and on the ten neighboring nuclei but negligible elsewhere.