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- Cobet, C, et al.
(författare)
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Optical properties of wurtzite AlxGa1-xN (x < 0.1) parallel and perpendicular to the c axis
- 2001
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 64:16
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of the dielectric function components parallel and perpendicular to the optical axis of wurtzite GaN are presented. The results are obtained on a multilayer AlxGa1-xN / GaN film grown on gamma -LiAlO2 which exhibits a very small amount of Al (x<0.1) in the uppermost layer. We use the spectroscopic ellipsometry to determine (omega) around the interband critical points of GaN up to 9 eV. Since the optical axis of the films are parallel to the surface, a separation of the different epsilon components is possible. The line shape of the measured tensor components e(parallel to) and epsilon (perpendicular to) is in very good agreement with results of recently published band-structure calculations. By comparison with the calculations we assign structures in the dielectric function to critical points in the Brillouin zone. In addition, a comparison with similar spectra for CdS and CdSe is presented, together with a discussion of possible spin-orbit splitting effects.
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- Schael, S, et al.
(författare)
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Precision electroweak measurements on the Z resonance
- 2006
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Ingår i: Physics Reports. - : Elsevier BV. - 0370-1573 .- 1873-6270. ; 427:5-6, s. 257-454
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Forskningsöversikt (refereegranskat)abstract
- We report on the final electroweak measurements performed with data taken at the Z resonance by the experiments operating at the electron-positron colliders SLC and LEP. The data consist of 17 million Z decays accumulated by the ALEPH, DELPHI, L3 and OPAL experiments at LEP, and 600 thousand Z decays by the SLID experiment using a polarised beam at SLC. The measurements include cross-sections, forward-backward asymmetries and polarised asymmetries. The mass and width of the Z boson, m(Z) and Gamma(Z), and its couplings to fermions, for example the p parameter and the effective electroweak mixing angle for leptons, are precisely measured: m(Z) = 91.1875 +/- 0.0021 GeV, Gamma(Z) = 2.4952 +/- 0.0023 GeV, rho(l) = 1.0050 +/- 0.0010, sin(2)theta(eff)(lept) = 0.23153 +/- 0.00016. The number of light neutrino species is determined to be 2.9840 +/- 0.0082, in agreement with the three observed generations of fundamental fermions. The results are compared to the predictions of the Standard Model (SM). At the Z-pole, electroweak radiative corrections beyond the running of the QED and QCD coupling constants are observed with a significance of five standard deviations, and in agreement with the Standard Model. Of the many Z-pole measurements, the forward-backward asymmetry in b-quark production shows the largest difference with respect to its SM expectation, at the level of 2.8 standard deviations. Through radiative corrections evaluated in the framework of the Standard Model, the Z-pole data are also used to predict the mass of the top quark, m(t) = 173(+10)(+13) GeV, and the mass of the W boson, m(W) = 80.363 +/- 0.032 GeV. These indirect constraints are compared to the direct measurements, providing a stringent test of the SM. Using in addition the direct measurements of m(t) and m(W), the mass of the as yet unobserved SM Higgs boson is predicted with a relative uncertainty of about 50% and found to be less than 285 GeV at 95% confidence level. (c) 2006 Elsevier B.V. All rights reserved.
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