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Charge and spin dynamics in the electron-doped high temperature superconducting cuprates
G. V. M. Williams,S. Kramer,R. Dupree 한국물리학회 2004 Current Applied Physics Vol.4 No.2-4
We show that the63Cu and17O NMR spin-lattice relaxation rates from the electron-doped high temperature superconducting cuprates (HTSC), Sr0:9La0:1CuO2 and Pr1:85Ce0:15CuO4 are consistent with antiferromagnetic spin uctuations in the CuO2 planes.However, unlike the hole-doped HTSC, there is no normal-state pseudogap or spin-gap. Furthermore, there is no evidence for aslowing down of the spin dynamics that is observed in underdoped and hole-doped HTSC and attributed to electronic phaseseparation. We also nd that the normal-state static spin susceptibility in Sr0:9La0:1CuO2 is only . 15% of that observed in the hole-doped HTSC.
X-ray and UV induced photo-luminescence from RbCdF3:Mn2+
G.V.M. Williams,S. Schweizer,B. Henke,C. Dunford,A. Edgar 한국물리학회 2006 Current Applied Physics Vol.6 No.3
We report the results from photo-luminescence (PL) measurements on single crystal RbCdF3 doped with up to 1% Mn2+, before andafter X-ray and deep UV irradiation. The intensity of the Mn2+ PL emission at 560 nm increases with increasing X-ray or UV (<270 nm)excited by this broad band is observed to increase with increasing radiation dose, and no signicant decrease in the PL intensity isobserved after 2 weeks. High intensity bleaching in the wavelength range from 280 nm to 420 nm reduces the PL emission to the originallow pre-irradiated level. These observations suggest that RbCdF3:Mn2+ has potential as a dosimeter for X-rays and deep UV wave-lengths less than 270 nm. We nd that the PL intensity systematically increases with increasing Mn2+ concentration and there is no evi-dence of saturation for up to 1% Mn2+. This indicates that higher sensitivity could occur with even higher concentrations of Mn2+.
Lithium borate glass ceramics as thermal neutron imaging plates
G.A. Appleby,C.M. Bartle,G.V.M. Williams,A. Edgar 한국물리학회 2006 Current Applied Physics Vol.6 No.3
A new glass ceramic composed of a lithium borate glass matrix containing Eu-doped BaCl2 crystals has been developed for thermalneutron radiography, and has been tested for sensitivity toc-radiation. It is shown to exhibit photostimulated luminescence (PSL) uponX- and c-irradiation. The PSL arises from orthorhombic BaCl2 nanocrystallites in the glass ceramics, which also contain a PSL-inactivephase of cubic BaCl2. The relative PSL eciency of the glass ceramics has a strong dependence on gamma energy, which correlates withrelative half-thickness. The eect of uoride doping in the glass ceramics has been found to substantially increase the PSL, which rangesfrom. 0.6% without uoride doping to. 8% with 0.2 F:Cl concentration, all relative to Fujilm’s commercial neutron imaging plateBAS-ND.
Tracking the pseudogap below Tc by modeling the Raman response
James G. Storey,Jeffery L. Tallon,Grant V.M. Williams 한국물리학회 2008 Current Applied Physics Vol.8 No.3,4
We calculate the B₁g and B₂g Raman responses of Bi-2212 from an ARPES-derived energy dispersion and a model for the normal-state pseudogap. The doping dependence is found to closely mimic the experimental data from a recent Raman study reporting the obser-vation of two distinct energy scales. In light of these calculations, the Raman data demonstrates that the pseudogap does not evolvegreatly below Tc.
Oxygen loading in second-generation high-temperature superconductor tapes
N.M. Strickland,G.V.M. Williams,Anita Semwal,D.T. Verebelyi,W. Zhang 한국물리학회 2006 Current Applied Physics Vol.6 No.3
We report a study of oxygen loading in YBa2Cu3O7. d coated conductors fabricated by metalorganic deposition. In situ X-ray dirac-tion experiments allowed the measurement of small changes in thec-axis lattice parameter during and after oxygen loading, and thesechanges could be correlated with the oxygen stoichiometry. The variation of the superconducting transition temperature and critical cur-oxygen loading. Optimum performance is therefore obtained by fully oxygen loading to an overdoped state.
NMR and electronic inhomogeneity in cuprate superconductors
J. Haase,G.V.M. Williams 한국물리학회 2006 Current Applied Physics Vol.6 No.3
interpretation of experiments and for theory. NMR is a very versatile method and we show that the NMR data clearly reveal that allcuprates, although to a very dierent extent, show inhomogeneity in the static charge and spin density. While part of the evidence makesthis inhomogeneity appear to be a variation of local doping, other NMR experiments show that the length-scales involved must be on theorder of a few CuCu distances. Estimates of the extent of these variations in dierent materials are given.
New materials for glass-ceramic X-ray storage phosphors
A. Edgar,M. Secu,S. Schweizer,J. -M. Spaeth,G. V. M. Williams,J. Hamlin 한국물리학회 2004 Current Applied Physics Vol.4 No.2-4
The development of transparent glass ceramics as X-ray storage phosphors and their advantages over their crystalline coun-terparts are briey reviewed. Measurements of conversion eciency, stimulation eciency, storage times, and optical transparencyare reported for the particular case of europium-doped uorobromozirconate glass, in which rubidium and lithium replace the usualsodium component fraction. Annealing at 280.C converts the as-prepared glass into a glassceramic which contains Rb2BaBr4 andRbBa2Br5 nano- and micro-crystallites. Only the RbBa2Br5 structure shows signicant photo-stimulated luminescence after X-irradiation, and the maximum storage phosphor eciency is 8% of that for the standard commercial storage phosphor BaFBr:Eu.
Spatial resolution of a glass-ceramic X-ray storage phosphor
A. Edgar,G.V.M. Williams,S. Schweizer,J.-M. Spaeth 한국물리학회 2006 Current Applied Physics Vol.6 No.3
The spatial resolution of a glass-ceramic X-ray storage phosphor imaging plate has been measured using a scanned and focussed laserbeam. The glass ceramic comprises orthorhombic phase barium chloride crystals containing europium ions embedded in a uorozirco-nate glass matrix. The modulation transfer function extends to signicantly higher frequencies than for a commercial imaging plate basedmercial plate. The modulation transfer function has a bimodal character which we ascribe to component responses from the focussedlaser beam volume and from the surrounding scattering halo. A limitation on performance of this particular glass ceramic is the occur-rence of bubbles and other defects which scatter the read-out light beam and reduce the uniformity of the response.
Radiation-induced optically and thermally stimulated luminescence in RbCdF3 and RbMgF3
C. Dotzler,G.V.M. Williams,A. Edgar 한국물리학회 2008 Current Applied Physics Vol.8 No.3,4
The optically stimulated luminescence (OSL) and thermoluminescence (TL) properties of the uoroperovskites RbCdF3 and RbMgF 3doped with manganese impurities are reported. Ionising radiation induces OSL excitation bands in the UV (310 nm) in these compounds.The corresponding OSL emission arises from the4T1g(G) to6A1g(S) electronic transition of Mn2+. The same PL emission is observed inTL measurements. The OSL is thermally stable up to 190.C in RbCdF3:Mn2+ and up to 260 .C in RbMgF 3:Mn2+. Possible mechanismsfor the observed eects are discussed.