Thermal destruction of spin-polaron bands in the narrow-gap correlated semiconductors FeGa3 and FeSb2.

We report muon spin rotation spectra in the narrow-gap semiconductors FeGa(3) and FeSb(2) consistent with a narrow band of small spin polarons (SPs). The characteristic sizes obtained for these SPs are R(FeGa(3)) ≈ 0.3-0.

GRID-ENABLED TREATMENT PLANNING FOR PROTON THERAPY USING MONTE CARLO SIMULATIONS.

Grid computing is an emerging technology that enables computational tasks to be accomplished in a collaborative approach by using a distributed network of computers. The grid approach is especially important for computationally intensive problems that are not tractable with a single computer or even with a small cluster of computers, e.g.

Bound magnetic polarons in the 3d-electron ferromagnetic spinel semiconductor CdCr2Se4.

Muon spin rotation/relaxation spectroscopy has been employed to study electron localization into a bound magnetic polaron around the positive muon in the 3d magnetic spinel semiconductor CdCr2Se4 at temperatures up to 300 K (far above the ferromagnetic transition at Tc = 130 K) in magnetic fields up to 7 T. Electron localization into a magnetic polaron occurs due to its strong exchange interaction with the magnetic 3d electrons of local Cr(3 +) ions, which confines its wavefunction to within R≈0.3 nm, allowing significant overlap with both the nearest and the next nearest shells of Cr ions.

Spin polarons in the correlated metallic pyrochlore Cd2Re2O7.

Muon spin rotation spectroscopy reveals localized electron states in the geometrically frustrated metallic pyrochlore Cd2Re2O7 at temperatures from 2 to 300 K in transverse magnetic fields up to 7 T. Two distinctive types of localized states, with characteristic radii of about 0.5 and 0.

The donor nature of muonium in undoped, heavily n-type and p-type InAs.

The charge state of muonium has been investigated in p-type doped, nominally undoped (low n-type) and heavily n-type doped InAs. The donor Mu(+) state is shown to be the dominant defect in all cases. Consequently, muonium does not simply counteract the prevailing conductivity in this material.

Hydrogen defect-level pinning in semiconductors: the muonium equivalent.

We have determined locations for the donor and acceptor levels of muonium in six semiconductor materials (Si, Ge, GaAs, GaP, ZnSe, and 6H-SiC) as a test of defect-level pinning for hydrogen. Within theoretical band alignments, our results indicate a common energy for the equilibrium charge-transition level Mu(+/-) to within experimental uncertainties. However, this is nearly 0.

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.

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 ( View Article and Find Full Text PDF

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.

Muonium analog of hydrogen passivation: observation of the Mu+-Zn- reaction in GaAs.

We report direct detection of the formation and subsequent breakup of a complex containing positively charged muonium ( Mu+) and a substitutional Zn(Ga) acceptor in heavily doped p-type GaAs:Zn. Mu+ diffuses above 200 K with a hop rate nu = nu(0)e(-E(nu)/k(B)T) where nu(0) = (7.7+/-2.

Experimental confirmation of the predicted shallow donor hydrogen state in zinc oxide.

We confirm the recent prediction that interstitial protium may act as a shallow donor in zinc oxide, by direct spectroscopic observation of its muonium counterpart. On implantation into ZnO, positive muons--chemically analogous to protons in this context--form paramagnetic centers below about 40 K. The muon-electron contact hyperfine interaction, as well as the temperature and activation energy for ionization, imply a shallow level.

Novel behavior of bond-centered muonium in heavily doped n-type silicon: Curie-like spin susceptibility and charge screening.

Bond-centered muonium ( Mu(0)(BC)) has been observed in very heavily doped n-type Si:P. It exhibits a Curie-like electronic spin susceptibility which leads to a giant negative shift in the muon spin precession frequency. At high dopant levels, the Mu(0)(BC) hyperfine parameters, deduced from a model involving spin exchange with free carriers, are significantly reduced from those in intrinsic Si.