Resolved nuclear hyperfine structure of muonium in CuCl by means of muon level-crossing resonance

Datailed muon level-crossing resonance measurements of Mu¹ and Mu¹¹ centres in single crystals of CuCl are presented. The hyperfine and nuclear hyperfine parameters of the closest two shells of nuclei are remarkably similar for the two centres, indicating that both are located at the same tetrahedral interstitial site with four Cu nearest neighbours and six Cl next-nearest neighbours. About 30% of the total unpaired-electron spin density is located on the muon, about 60% on the four nearest neighbours and the rest on the six next-nearest neighbours, with nothing observable for any other shell.     

Muon bonding versus muonium formation: Muon-Spin-Relaxation in α-Al2O3

Results of Muon-Spin-Relaxation (μSR) experiments on well-defined single crystals of corundum (α-Al₂O₃) are reported. Major issue in this study is the controversy of muon bonding or muonium formation in insulators. Transverse, zero-field and longitudinal field measurements were performed as a function of temperature or applied field. The obtained results indicate that muon-oxygen bonding occurs in α-Al₂O₃, having (at least) two (μO) states as found earlier for α-Fe₂O₃. The occurrence of a 10% missing fraction suggests Mu states, although Mu was not observed in our measurements. These results and their implications are discussed in light of other experimental μSR studies on insulating oxides and the above-mentioned controversy.     

Muon level crossing resonance in niobium

A useful guide to detecting quadrupole level crossing resonance (QLCR) spectra is to search in the vicinity of B_E\cdot(\gamma_n/\gamma_μ), where B_E is the onset magnetic field for the decoupling of the quadrupole interaction, as seen in muon spin rotation linewidths. More detailed predictions of the positions and intensities of the resonances require numerical simulations taking account of the local geometry of the muon site. We present such simulations for muons adjacent to nuclei of spin 9/2 and demonstrate a pronounced dependence on the anisotropy of the quadrupole coupling tensor. Simulations for the specific cases of muons located at the octahedral and tetrahedral interstices in niobium metal are compared with the experimentally detected spectrum in a polycrystalline sample. This revised version was published online in August 2006 with corrections to the Cover Date.