Influence of impurities on short range electron transport in GaAs

The influence of Cr impurities on muonium atom formation in GaAs has been studied using muon spin relaxation techniques with alternating electric fields. The results suggest that electron transport to and capture by the muon is suppressed by capture/scattering on intervening Cr centers. The length scale involved is estimated to be about 3x10(-6) cm. This offers an opportunity to study electron transport to positive centers in semiconductors on a microscopic scale.     

Local structure of isolated positively charged muonium as an analog for the hydrogen ion in p-type GaAs

We determine the local structure of isolated positively charged muonium (Mu+) in heavily doped p-type GaAs based on muon level crossing resonance and zero applied field muon spin depolarization data. These measurements provide the first direct experimental confirmation that Mu+, and by analogy H+, is located within a stretched Ga-As bond. The distances between Mu+ and the nearest neighbor Ga and As atoms are estimated to be 1.83 +/- 0.10 A; and 1.76 +/- 0.10 A, respectively. These results are compared to existing theoretical calculations on the structure of hydrogen in GaAs and additionally provide data on the induced electric field gradients.     

Muonium as a shallow center in GaN

A paramagnetic muonium (Mu) state with an extremely small hyperfine parameter was observed for the first time in single-crystalline GaN below 25 K. It has a highly anisotropic hyperfine structure with axial symmetry along the <0001> direction, suggesting that it is located either at a nitrogen-antibonding or a bond-centered site oriented parallel to the c axis. Its small ionization energy (相似文献   

Muonium dynamics in transparent conducting oxides

The motional and electrical properties of positively charged muonium (Mu⁺)$({\mathrm{Mu}}^{+})$ centers in single crystal β-Ga₂O₃$\mathrm{\beta }\mathrm{-}{\mathrm{Ga}}_2{\mathrm{O}}_3$ are investigated via zero field muon spin relaxation (ZF-MuSR). Below room temperature we find two distinct shallow muonium centers with ionization energies of 7 and 16 meV. Above room temperature, at least three different Mu⁺ signals are resolved; two of these are metastable while the third shows characteristics of a stable ground state. As the temperature is elevated, metastable centers undergo several transitions. We obtain the relevant barrier energies associated with these site-change transitions. By 700 K, most muons occupy the mobile ground state, and an activation energy of about 1.65 eV is inferred for Mu⁺ diffusion from the hop rates obtained for this state.     

Observation of the anisotropic spin-glass transition and transverse spin ordering in pseudo-brookite through muon spin relaxation

Zero-field longitudinal muon-spin-relaxation (μSR) experiments have been performed on single crystals of pseudo-brookite (Fe₂−_xTi_l+x ^O ₅; x=0.25), an anisotropic spin-glass system. The spinglass temperature (Tg) is determined to be 44.0±0.5K. Above Tg, a distinct exponential muon-spin-relaxation rate (λ) is observed, while below Tg a square-root exponential decay is seen, indicating fast spin fluctuations in the ‘frozen’ state. Near 8K, a maximum in λ is observed, which is due to transverse spin ordering at these low temperatures. Even near Tg, λ is very low (<1 μs⁻¹), likely due to a well-defined muon-oxygen state in the single crystals. The sharp λ-increase (with decreasing temperatures) above Tg allows a comparison between spinfreezing models like the Vogel-Fulcher law and a power law. The results of these initial measurements indicate that dynamic (and static) magnetism in oxide spin glasses can be directly monitored through μSR.     

Spin-cluster effects and frustration in the uniaxial spin glass Fe2−xTi1+xO5

Transverse-field (TF) muon-spin-relaxation (μSR) and Mössbauer experiments on the uniaxial insulating spin glass Fe_2?xTi_1+xO₅ (x=0.25) have been performed near and below the spin-glass temperature (T _g). The effect of a transverse field on the spin-freezing process and spin-glass state has been investigated by measuring the field-and temperature-dependencies of the μSR parameters. Spin-cluster effects signaled by anomalous μ-spin relaxation have been observed in a temperature region just aboveT _g. An interpretation supported by recently developed theoretical models addressing non-linear relaxation in an intermediate Griffiths phase is offered.     

Muon-oxygen bonding in V2O3

A muon site search using calculated internal fields has been performed for V₂O₃, where purely dipolar fields allow a site determination free from covalent complications. The obtained sites are a subset of the Rodriguez and Bates sites found in α-Fe₂O₃ and indicate muon oxygen bond formation. The sites missing at low temperatures are consistent with the vanadium pairing mechanism for the metal-to-insulator (corundum-to-monoclinic) phase transition.     

Diamagnetic muonium states in InP

Transverse and zero‐field muon spin relaxation reveal several diamagnetic muonium states in InP characterized by their static linewidths and diffusion properties. We tentatively associate low‐temperature diamagnetic states with Mu⁺ in the BC and T_P interstitial sites and a missing fraction with Mu⁰ rapidly diffusing through T_In interstices. Trapping peaks above 250 K imply static centers which depend on doping type, consistent with Mu^- at T_In for n‐type samples and Mu coupled with a dopant or other defect for p‐type. This revised version was published online in August 2006 with corrections to the Cover Date.