15 research outputs found
Low field vortex matter in YBCO: an atomic beam magnetic resonance study
We report measurements of the low field structure of the magnetic vortex
lattice in an untwinned YBCO single-crystal platelet. Measurements were carried
out using a novel atomic beam magnetic resonance (ABMR) technique. For a 10.7 G
field applied parallel to the c-axis of the sample, we find a triangular
lattice with orientational order extending across the entire sample. We find
the triangular lattice to be weakly distorted by the a-b anisotropy of the
material and measure a distortion factor, f = 1.16. Model-experiment
comparisons determine a penetration depth, lambda_ab = 140 (+-20) nm. The paper
includes the first detailed description of the ABMR technique. We discuss both
technical details of the experiment and the modeling used to interpret the
measurements.Comment: 44 pages, 13 figures, submitted to Phys. Rev. B Revision includes
Postscript wrapped figures + minor typo
Localization by disorder in the infrared conductivity of (Y,Pr)Ba2Cu3O7 films
The ab-plane reflectivity of (Y{1-x}Prx)Ba2Cu3O7 thin films was measured in
the 30-30000 cm-1 range for samples with x = 0 (Tc = 90 K), x = 0.4 (Tc = 35 K)
and x = 0.5 (Tc = 19 K) as a function of temperature in the normal state. The
effective charge density obtained from the integrated spectral weight decreases
with increasing x. The variation is consistent with the higher dc resistivity
for x = 0.4, but is one order of magnitude smaller than what would be expected
for x = 0.5. In the latter sample, the conductivity is dominated at all
temperatures by a large localization peak. Its magnitude increases as the
temperature decreases. We relate this peak to the dc resistivity enhancement. A
simple localization-by-disorder model accounts for the optical conductivity of
the x = 0.5 sample.Comment: 7 pages with (4) figures include
Optical symmetries and anisotropic transport in high-Tc superconductors
A simple symmetry analysis of in-plane and out-of-plane transport in a family
of high temperature superconductors is presented. It is shown that generalized
scaling relations exist between the low frequency electronic Raman response and
the low frequency in-plane and out-of-plane conductivities in both the normal
and superconducting states of the cuprates. Specifically, for both the normal
and superconducting state, the temperature dependence of the low frequency
Raman slope scales with the axis conductivity, while the
Raman slope scales with the in-plane conductivity. Comparison with experiments
in the normal state of Bi-2212 and Y-123 imply that the nodal transport is
largely doping independent and metallic, while transport near the BZ axes is
governed by a quantum critical point near doping holes per
CuO plaquette. Important differences for La-214 are discussed. It is also
shown that the axis conductivity rise for is a consequence of
partial conservation of in-plane momentum for out-of-plane transport.Comment: 16 pages, 8 Figures (3 pages added, new discussion on pseudogap and
charge ordering in La214
Membrane catalysts in selective hydrogenation of certain products of pyrolysis of petroleum hydrocarbons
[No abstract available
Membrane catalysts in selective hydrogenation of certain products of pyrolysis of petroleum hydrocarbons
[No abstract available