Muonium states in silicon carbide

Implanted muons in samples of silicon carbide have been observed to form paramagnetic muonium centers (μ ⁺ e⁻). Muonium precession signals in low applied magnetic fields have been observed at 22 K in a granular sample of cubic β-SiC, however it was not possible to determine the hyperfine frequency. In a single crystal sample of hexagonal 6H-SiC, three apparently isotropic muonium states were observed at 20 K and two at 300 K, all with hyperfine frequencies intermediate between those of the isotropic muonium centers in diamond and silicon. No evidence was seen of an anisotropic muonium state analogous to the Mu^* state in diamond and silicon.     

Molecular reorientation of liquid silicon tetrachloride

The phase diagram of a two dimensional system of hard cyclic hexamers is studied using a constant pressure Monte Carlo method in which the shape and size of the periodic box containing molecules are allowed to vary. This system exhibits a variety of phases in agreement with previous mechanical simulations.     

Muonium

Muonium, the bound state of the two structureless leptons μ⁺ and e⁻, is an ideal system to test quantum electrodynamics and tiny contributions of other interactions. This paper reviews the latest state of the measurements and theories for the muonium hyper-fine structure in the ground state and the 1S–2S splitting in muonium. The results of these experiments are indispensable to interpret a more precise measurement of the anomalous magnetic moment of the muon presently underway. Furthermore, the search for muonium-antimuonium conversion is reported and discussed with respect to lepton number conservation.     

Muonium in ice

Muonium has been studied in single crystals of H₂O and D₂O. Two-frequency precession in low transverse fields and a single zero-field oscillation indicate a small anisotropy of axial symmetry in the muonium hyperfine interaction. The anisotropy is shown to be the cause of the hitherto unexplained temperature independent contribution to muonium spin relaxation in polycrystalline samples. Relaxation rates for 99 K–263 K are reported for muonium in a single crystal of H₂O. Relaxation is attributed to electron-nuclear dipolar coupling of muonium to lattice protons, modulated by translational diffusion of muonium alongc-axis channels of the ice lattice. A simple model for H and Mu diffusion in ice is investigated.This work was supported by the Natural Sciences and Engineering Research Council of Canada through an Intermediate Energy Physics Project Grant.     

Muonium spectroscopy

The electromagnetic interactions of electrons and muons can be described to very high accuracy within the framework of standard theory, in particular within the hydrogen like muonium atom. Therefore, precision measurements are able to test basic interactions in physics and to search for yet unknown forces. Accurate values for fundamental constants can be obtained. Results from experiments on the ground state hyperfine structure and the 1s–2s intervals in muonium are described together with their relations to a new measurement of the muon magnetic anomaly. This revised version was published online in August 2006 with corrections to the Cover Date.     

Muonium acoustic resonance

Theoretical consideration is given to the effect of ultrasonic oscillations on the spin polarization of the positive muon of muonium present in matter. The resonant action of the periodic acoustic perturbation on the muonium hyperfine structure levels is shown to result in characteristic oscillations and to modify the muon spin precession pattern considerably. The possibilities for experimental detection of the muonium acoustic resonance are discussed     

Muonium and micelles

A pseudo first-order term has been added to the kinetic analysis of micelle-mediated muonium reactions. It is discussed with respect to enhancements of several orders of magnitude for reactions such as that of 2-propanol. It covers the possibility of ‘trapping’ of muonium followed by tunneling.     

Muonium radicals in benzene-styrene mixtures

Muonium radicals were observed through theirSR precession frequencies in high transverse magnetic fields in pure benzene, pure styrene and their mixtures, all as liquids at room temperature. In benzene-styrene mixtures, the radicals obtained in each pure liquid are both present, so no slow (10^–9–10^–5 s) intermolecular exchange occurs; but strong selectivity was found with the formation of the radical from styrene being about eight-times more probable than the radical from benzene.     

Muonium quantum diffusion in cryocrystals

In this paper we review our recent study on muonium (Mu) diffusion in simplest solids — Van der Waals cryocrystals. We give experimental evidence for the quantum nature of Mu diffusion in these matters. The results are compared with the current theory of quantum diffusion in insulators. The first direct observation of theT ⁷ power-law for the Mu hop rate (in solid nitrogen) is taken as confirmation of two-phonon scattering mechanism. In solid xenon the one-phonon interaction is shown to be dominant. Muonium diffusion in solid neon is discussed in terms of band-like motion. Finally, we report a dramatic effect of impurities on Mu quantum diffusion.     

Muonium defect centers in semiconductors

After a brief summary of the properties of the muonium defect centers observed in the elemental group IV semiconductors, the status of studies of muonium centers in semiconductors at the time of the last μSR conference in 1983 will be compared with what is currently known. With the introduction of new experimental techniques, such as high-transverse-field μSR and level-crossing spectroscopy, many new results are or soon will be available on muonium centers. These, combined with new theoretical studies, should lead to rapidly increased insight into a subject which has been both puzzling and resistant to clarification.     

Muonium and hydrogen in semiconductors

As impurities in semiconductors muonium and hydrogen should have many similarities. In principle properties such as structures which depend primarily on their identical adiabatic potential energies should be much the same while dynamic characteristic such as diffusion would be quite different. The experimental results are in fact quite different for the two but for other reasons. This paper indicates something of the current interest in hydrogen impurities, which is mostly focussed on passivation and hydrogen pairs with other impurities or intrinsic defects, and then discusses muonium in semiconductors, where the abundant information has to do with the isolated impurity. Consequently a complete picture of hydrogen/muonium at the moment requires the study of both.     

Muonium states in zincblende-structured compounds

The authors present a list of results of μSR experiments in materials with the diamond and zincblende structure. Besides the muonium hyperfine parameters, additional information is tabulated: the formation probability for the different muon states, the highest temperatures at which muonium states have been observed and the types of transitions found to occur between these states. The muonium hyperfine parameters show a linear rise as a function of host ionicity from Ge to GaAs to ZnSe followed by a sharp drop to CuBr.     

Muonium substituted hydrazyl radicals

Hyperfine coupling constants for muonium substitited hydrazyl radicals are reported. They are compared with the existing data for the hydrogen analogs. The influence of the temperature and the solvent are given.