315 research outputs found
Plasma Waves in Anisotropic Superconducting Films Below and Above the Plasma Frequency
We consider wave propagation inside an anisotropic superconducting film
sandwiched between two semi-infinite non-conducting bounding dieletric media
such that along the c-axis, perpendicular to the surfaces, there is a plasma
frequency below the superconducting gap. Propagation is assumed to
be parallel to the surfaces in the dielectric medium, where amplitudes decay
exponentially.Below , the amplitude also evanesces inside the film,
and we retrieve the experimentally measured lower dispersion relation branch,
, and the recently proposed higher frequency
branch, .Above , propagation is of the
guided wave type, i.e., a dispersive plane wave confined inside the film that
reflects into the dielectric interfaces,and the modes are approximately
described by , where
is discussed here.Comment: 26 pages,4 figures.Submitte
Explaining the x-ray nonlinear susceptibility of diamond and silicon near absorption edges
International audienceWe report the observation and the theoretical explanation of the parametric down-conversion nonlinear susceptibility at the K-absorption edge of diamond and at the L 23-absorption edge of a silicon crystal. Using arguments similar to those invoked to successfully predict resonant inelastic x-ray spectra, we derive an expression for the renormalization term of the nonlinear susceptibility at the x-ray edges, which can be evaluated by using first-principles calculations of the atomic scattering factor f 1. Our model is shown to reproduce the observed enhancement of the parametric down-conversion at the diamond K and the Si L 23 edges rather than the suppression previously claimed
Results of a Search for Paraphotons with Intense X-ray Beams at SPring-8
A search for paraphotons, or hidden U(1) gauge bosons, is performed using an
intense X-ray beamline at SPring--8. "Light Shining through a Wall" technique
is used in this search. No excess of events above background is observed. A
stringent constraint is obtained on the photon--paraphoton mixing angle, for .Comment: 10 pages, 4 figure
Recoil effects of photoelectrons in a solid
High energy resolution C 1 photoelectron spectra of graphite were measured
at the excitation energy of 340, 870, 5950 and 7940eV using synchrotron
radiation. On increasing the excitation energy, i.e., increasing kinetic energy
of the photoelectron, the bulk origin C 1 peak position shifts to higher
binding energies. This systematic shift is due to the kinetic energy loss of
the high-energy photoelectron by kicking the atom, and is clear evidence of the
recoil effect in photoelectron emission. It is also observed that the
asymmetric broadening increases for the higher energy photoelectrons. All these
recoil effects can be quantified in the same manner as the M\"ossbauer effect
for -ray emission from nuclei embedded in crystals.Comment: 4 pages, 2 figure
Planar hole-doping concentration and effective three-dimensional hole-doping concentration for single-layer high- superconductors
We propose that physical properties for the high temperature superconductors
can be addressed by either a two-dimensional planar hole-doping concentration
() or an effective three-dimentional hole-doping concentration
(). We find that superconducting transition temperature ()
exhibits a universal dome-shaped behavior in the plot with
a universal optimal doping concentration at 1.6
10 cm for the single-layer high temperature superconductors.Comment: 2pages, 2 figures, submitted to Physica C (Proceedings of M2S-HTSC
VIII) ; Ref. 10 is revise
Itinerant Ferromagnetism in layered crystals LaCoOX (X = P, As)
The electronic and magnetic properties of cobalt-based layered oxypnictides,
LaCoOX (X = P, As), are investigated. LaCoOP and LaCoOAs show metallic type
conduction, and the Fermi edge is observed by hard x-ray photoelectron
spectroscopy. Ferromagnetic transitions occur at 43 K for LaCoOP and 66 K for
LaCoOAs. Above the transition temperatures, temperature dependence of the
magnetic susceptibility follows the Curie-Weiss law. X-ray magnetic circular
dichroism (XMCD) is observed at the Co L2,3-edge, but not at the other edges.
The calculated electronic structure shows a spin polarized ground state. These
results indicate that LaCoOX are itinerant ferromagnets and suggest that their
magnetic properties are governed by spin fluctuation.Comment: 16 pages, 9 figures, Physical Review B, in press. Received 17
February 2008. Accepted 29 May 200
High efficiency and low absorption Fresnel compound zone plates for hard X-ray focusing
Circular and linear zone plates have been fabricated on the surface of
silicon crystals for the energy of 8 keV by electron beam lithography and deep
ion plasma etching methods. Various variants of compound zone plates with
first, second, third diffraction orders have been made. The zone relief height
is about 10 mkm, the outermost zone width of the zone plate is 0.4 mkm. The
experimental testing of the zone plates has been conducted on SPring-8 and ESRF
synchrotron radiation sources. A focused spot size and diffraction efficiency
measured by knife-edge scanning are accordingly 0.5 mkm and 39% for the first
order circular zone plate.Comment: 5 pages, 7 figure
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