196 research outputs found
The unusual morphology, structure, and magnetic property evolution of glassy carbon upon high pressure treatment
High pressure synthesis of a new superconductor Sr2CuO2+xCl2-y induced by apical oxygen doping
Using the apical oxygen doping mechanism, i.e. a partial substitution of
divalence O for the monovalence Cl, a p-type oxychloride cuprate
superconductor, Sr2CuO2+xCl2-y, was synthesized at high pressure high
temperature. The x-ray diffraction refinement suggests the superconductor
crystallizes into a 0201 structure with space group I4/mmm and lattice
parameters being a=3.92A, c=15.6 A. The magnetic susceptibility as well as
resistance measurements indicated that the bulk superconductivity with
transition temperature 30K was achieved in the sample.Comment: accepted by physica
Multiple superconducting gap and anisotropic spin fluctuations in iron arsenides: Comparison with nickel analog
We present extensive 75As NMR and NQR data on the superconducting arsenides
PrFeAs0.89F0.11 (Tc=45 K), LaFeAsO0.92F0.08 (Tc=27 K), LiFeAs (Tc = 17 K) and
Ba0.72K0.28Fe2As2 (Tc = 31.5 K) single crystal, and compare with the nickel
analog LaNiAsO0.9F0.1 (Tc=4.0 K) . In contrast to LaNiAsO0.9F0.1 where the
superconducting gap is shown to be isotropic, the spin lattice relaxation rate
1/T1 in the Fe-arsenides decreases below Tc with no coherence peak and shows a
step-wise variation at low temperatures. The Knight shift decreases below Tc
and shows a step-wise T variation as well. These results indicate spinsinglet
superconductivity with multiple gaps in the Fe-arsenides. The Fe
antiferromagnetic spin fluctuations are anisotropic and weaker compared to
underdoped copper-oxides or cobalt-oxide superconductors, while there is no
significant electron correlations in LaNiAsO0.9F0.1. We will discuss the
implications of these results and highlight the importance of the Fermi surface
topology.Comment: 6 pages, 11 figure
The superconductivity at 18 K in LiFeAs system
A new iron arsenide superconducting system LiFeAs was found that crystallizes
into a tetragonal structure with space group P4/nmm. The superconductivity with
Tc up to 18 K was observed in the compounds. This simple 111 type layered iron
arsenide superconductor can be viewed as an analogue of the infinite layer
structure of copper oxides.Comment: 11 pages 3 Figure
Superradiance of low density Frenkel excitons in a crystal slab of three-level atoms: Quantum interference effect
We systematically study the fluorescence of low density Frenkel excitons in a
crystal slab containing V-type three-level atoms. Based on symmetric
quasi-spin realization of SU(3) in large limit, the two-mode exciton
operators are invoked to depict various collective excitations of the
collection of these V-type atoms starting from their ground state. By making
use of the rotating wave approximation, the light intensity of radiation for
the single lattice layer is investigated in detail. As a quantum coherence
effect, the quantum beat phenomenon is discussed in detail for different
initial excitonic states. We also test the above results analytically without
the consideration of the rotating wave approximation and the self-interaction
of radiance field is also included.Comment: 18pages, 17 figures. Resubmit to Phys. Rev.
Pressure dependence of the superconducting transition temperature of the filled skutterudite YFe4P12
We have studied the pressure dependence of the superconducting transition temperature Tc of the filled skutterudite YFe4P12 under various quasihydrostatic pressures up to 8 GPa. DC magnetization measurements up to 1.2 GPa in a piston-cylinder cell yields a linear increase of Tc with a positive coefficient dTc/dP = 1 K/GPa. Resistivity measurements up to 8 GPa in a cubic anvil apparatus show that Tc increases to 9.3 K at 8 GPa, but the slope decreases gradually with increasing pressure. Besides the previously reported LaFe4P12, YFe4P12 becomes the second filled skutterudite superconductor that exhibits a positive pressure coefficient dTc/dP in a broad pressure range. The observed large dTc/dP > 0 of YFe4P12 can be rationalized by our band-structure calculations that show an enhancement of density of states at Fermi energy and the Hopfield parameter under pressure at least up to 8 GPa. On the other hand, similar calculations predict a dTc/dP < 0 for YRu4P12
Studies on the formation and synthetic mechanism of related substance G in potassium clavulanate production
Measurement of the Atmospheric Muon Spectrum from 20 to 3000 GeV
The absolute muon flux between 20 GeV and 3000 GeV is measured with the L3
magnetic muon spectrometer for zenith angles ranging from 0 degree to 58
degree. Due to the large exposure of about 150 m2 sr d, and the excellent
momentum resolution of the L3 muon chambers, a precision of 2.3 % at 150 GeV in
the vertical direction is achieved.
The ratio of positive to negative muons is studied between 20 GeV and 500
GeV, and the average vertical muon charge ratio is found to be 1.285 +- 0.003
(stat.) +- 0.019 (syst.).Comment: Total 32 pages, 9Figure
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