A.S. Baturin

Relaxation equation for muonium-like systems with electron spin more than one half

Abstract A phenomenological derivation of the Wangsness–Bloch–Redfield equation for the density matrix of muonium-like systems is given in this paper. In the case of the isotropic relaxation, it is shown that the corresponding relaxation term is described by only two independent constants. A typical form of the density matrix of the isotropic hyperfine interaction is given, and it is shown that the density matrix is decomposed into diagonal blocks. Relaxation rates corresponding to the different blocks can differ by orders of magnitude.

Muonium and muonium-like systems formation in spur model

Abstract Track electron kinetics is shown to be important for the correct understanding of μSR experiments. The quasi-neutrality restoring time for the region of muon or meso-ion location is investigated theoretically and numerically in different models relating to positive and negative muons. Simple approximate formulae for numerical results are presented. This time is found to be much less than the muons lifetime for light gases and Ne at a liquid phase pressure. The foregoing makes it possible that meso-ion and electron interaction leads to the formation of Mu or muonium-like systems.

Muonic atom as an acceptor centre in diamond

Polarized negative muons were used to study the behaviour of the boron acceptor centre in diamond produced by the chemical vapour deposition (CVD) method. The temperature dependence of the muon spin relaxation rate and spin precession frequency were measured in the range of 20 – 330 K in a transverse magnetic field of 14 kOe. The muon polarization amplitude P(t = 0) does not depend on the temperature and the muon spin relaxation rate decreases as the temperature increases. For the first time a negative shift of the muon spin precession was observed in diamond. The measurements show that the magnetic susceptibility of the CVD sample is negligible (χ = -4.13(2)10−7cm3/g at 20 K) and it could not be the reason of the negative shift muon spin precession frequency. The negative shift of the muon spin precession frequency is tentatively attributed to an anisotropic hyperfine interaction in the boron acceptor in diamond.Polarized negative muons were used to study the behaviour of the boron acceptor centre in synthetic diamond produced by the chemical vapour deposition (CVD) method. The negative muon substitutes one of the electrons in a carbon atom, and this muonic atom imitates the boron acceptor impurity in diamond. The temperature dependence of the muon spin relaxation rate and spin precession frequency were measured in the range of 20− 330 K in a transverse magnetic field of 14 kOe. For the first time a negative shift of the muon spin precession was observed in diamond. It is tentatively attributed to an anisotropic hyperfine interaction in the boron acceptor. The magnetic measurements showed that the magnetic susceptibility of the CVD sample was close to that of the purest natural diamond. Diamond with its unsurpassed mechanical strength, thermal conductivity, and radiation hardness is a promising semiconductor for particle detectors and electronic components capable of withstanding high heat and radiation loads. Great advances have been made over the last years in the technology of manufacturing synthetic single crystal diamond and diamond films [1, 2, 3]. Boron is the only dopant which forms an acceptor centre (AC) in diamond with an ionization energy of ≈ 370 meV [4]. The metal-insulator transition occurs at a concentration of ≈ 2 · 10 cm of boron atoms [5]. The EPR signal of boron impurities in diamond was observed only for uniaxially stressed samples [6], and the electronic state of this acceptor is investigated insufficiently. The possibility of using negative muons to study the behaviour of acceptor impurities in diamond arises from the fact that capture of a negative muon by a carbon atom results in the formation of a muonic atom μB with an electron shell that is analogous to that of the boron atom. The evolution of the polarization of μ− in the 1s atomic state depends on the interaction of the muon spin with the electron shell of the muonic atom and on the interactions of this muonic atom

Calculation of the charge-carrier mobility in diamond at low temperatures

The discrepancies between the quasi-elastic and inelastic approaches to the calculation of the electron and hole mobilities in diamond at low temperatures when the carrier scattering from acoustic phonons becomes significantly inelastic have been numerically estimated. The calculations showed that the mobility described by a close-to-equilibrium distribution function differs several times from that obtained within the quasi-elastic approach even at 20 K. The results obtained are important for interpreting the low-temperature electrical experiments on high-purity diamond single crystals.

Measurement of the g-factor of the negative muon in the 1s-state of Zn and Cd atoms

Precise measurement of the anomalous g-value, am ¼ð g � 2Þ=2; of the negative muon boundin an atom provid es a sensitive test on the validity of: (1) the relativistic correction to g; (2) the quantum electrodynamics correction in a strong Coulomb fieldof the nucleus. In this work the magnetic moment of the negative muon in the 1s-state of Zn and Cd atoms was measured. A substantial deviation of the experimental data from the results of theoretical calculations is found. Possible reasons of this disagreement are discussed. r 2002 Elsevier Science B.V. All rights reserved.

Relaxation of the shallow acceptor center in germanium

Polarized negative muons were used to study relaxation mechanisms of shallow acceptors in germanium. In p-type germanium at low temperatures relaxation of the muon spin was observed, indicating that the muonic atom (gallium-like acceptor center) formed via capture of the negative muon by a host atom is in the paramagnetic state and its magnetic moment is relaxing. The relaxation rate of the muon spin was found to depend on temperature and on concentration of gallium impurity. We conclude that to the relaxation of the magnetic moment of the Ga acceptor in Ge there contribute both scattering of phonons and quadrupole interaction between the acceptors. We estimate, for the first time, the hyperfine interaction constant for the gallium acceptor in germanium as 0.11 MHz.

Application of μSR2 method to estimate the size of diamagnetic domains

Abstract μSR histograms obtained from different regions of a target have to be slightly different since magnetic fields are inhomogeneous. Calculation of a correlation function of these histograms allows to estimate the correlation radius of inhomogeneities. This method was named μSR 2 . Application of the μSR 2 method for estimating the sizes of magnetic domains is analyzed. Results of the computer simulation of a μSR 2 experiment to measure domain sizes are given. It is shown that domain sizes can be estimated within the accelerator operating time allocated for a conventional μSR experiment.