542 research outputs found
The color of polarization in cuprate superconductors
A technique for the identification of individual anisotropic grains in a heterogeneous and opaque material involves the observation of grain color in reflected light through crossed polarizers (color of polarization). Such colors are generally characteristic of particular phases. When grains of many members of the class of hole carrier cuprate superconductors are so viewed, using a xenon light source (600 K color temperature), a characteristic color of polarization is observed. This color was studied in many of these cuprate superconductors and a strong correlation was found between color and the existence of superconductivity. One of the members of the electron carrier cuprate superconductors (Nd(1.85)Ce(.15)CuO(4-x) was examined and found that it possesses the same color of polarization as all the electron hole carrier cuprate superconductors so far examined. The commonality of the characteristic color in the cuprate superconductors indicated that the presence of this color is independent of the nature of charge carriers. The correlation of this color with existence of superconductivity suggests that the origin of the color relates to the origin of superconductivity in the cuprate superconductors. Photometric techniques are also discussed
Dipole-dipole interaction of Josephson diamagnetic moments
The role of dipole-dipole interaction between Josephson diamagnetic moments
is considered within a model system of two clusters (each cluster contains
three weakly connected superconducting grains). The sign of the resulting
critical current is shown to depend on the orientation between clusters,
allowing for both 0 and type junctions behavior. The possibility of the
experimental verification of the model predictions is discussed
Upper Critical Field in a Spin-Charge Separated Superconductor
It is demonstrated that the spatial decay of the pair propagator in a
Luttinger liquid with spin charge separation contains a logarithmic correction
relative to the free fermi gas result in a finite interval between the spin and
charge thermal lengths. It is argued that similar effects can be expected in
higher dimensional systems with spin charge separation and that the temperature
dependence of the upper critical field curve is a probe of this
effect.Comment: 3 pages, postscript file (compressed and uuencoded
Quantum Resistive Transition in Type II Superconductors under Magnetic Field
It is shown that, within a Ginzburg-Landau (GL) formalism, the
superconducting fluctuation is insulating at zero temperature even if the
fluctuation dynamics is metallic (dissipative). Based on this fact, the low
temperature behavior of the -line and the resistivity curves near a
zero temperature transition are discussed. In particular, it is pointed out
that the neglect of quantum fluctuations in data analysis of the dc resistivity
may lead to an under-estimation of the values near zero temperature.Comment: 7 page
Potential Major Improvement in Superconductors for High-Field Magnets
Fusion reactors are limited by the magnetic field available to confine their
plasma. The commercial fusion industry uses the larger magnetic field and
higher operating temperature of the cuprate superconductor
(YBCO) in order to confine their plasma
into a dense volume. A superconductor is a macroscopic quantum state that is
protected from the metallic (resistive) state by an energy gap. Unfortunately,
YBCO has an anisotropic gap, known as D-wave because it has the shape of a
chemical orbital. This D-wave gap means that
poly-crystalline wire cannot be made because a few degree misalignment between
grains in the wire leads to a drastic loss in its supercurrent carrying
ability, and thereby its magnetic field limit. The superconductor industry has
responded by growing nearly-single-crystal superconducting YBCO films on
carefully prepared substrate tapes kilometers in length. Heroic development
programs have made such tapes commercially available, but they are very
expensive and delicate. MRI magnet superconductors, such as and
, are formed into poly-crystalline wires because they have
an isotropic gap in the shape of an s chemical orbital (called S-wave) that
makes them insensitive to grain misalignment. However, these materials are
limited to lower magnetic fields and liquid-He temperatures. Here, we modified
YBCO by doping the Y site with Ca and Ce atoms to form
, and show evidence
that it changes to an S-wave gap. Its superconducting transition temperature,
, of , while lower than that of D-wave YBCO at
, is easily maintained using common, economic cryogenic
equipment.Comment: 28 pages, 23 figure
Parameter-free expression for superconducting Tc in cuprates
A parameter-free expression for the superconducting critical temperature of
layered cuprates is derived which allows us to express Tc in terms of
experimentally measured parameters. It yields Tc values observed in about 30
lanthanum, yttrium and mercury-based samples for different levels of doping.
This remarkable agreement with the experiment as well as the unusual critical
behaviour and the normal-state gap indicate that many cuprates are close to the
Bose-Einstein condensation regime.Comment: 5 pages, 2 figures. Will be published in Physical Review
Evaluating the potential for the environmentally sustainable control of foot and mouth disease in Sub-Saharan Africa
Strategies to control transboundary diseases have in the past generated unintended negative consequences for both the environment and local human populations. Integrating perspectives from across disciplines, including livestock, veterinary and conservation sectors, is necessary for identifying disease control strategies that optimise environmental goods and services at the wildlife-livestock interface. Prompted by the recent development of a global strategy for the control and elimination of foot-and-mouth disease (FMD), this paper seeks insight into the consequences of, and rational options for potential FMD control measures in relation to environmental, conservation and human poverty considerations in Africa. We suggest a more environmentally nuanced process of FMD control that safe-guards the integrity of wild populations and the ecosystem dynamics on which human livelihoods depend while simultaneously improving socio-economic conditions of rural people. In particular, we outline five major issues that need to be considered: 1) improved understanding of the different FMD viral strains and how they circulate between domestic and wildlife populations; 2) an appreciation for the economic value of wildlife for many African countries whose presence might preclude the country from ever achieving an FMD-free status; 3) exploring ways in which livestock production can be improved without compromising wildlife such as implementing commodity-based trading schemes; 4) introducing a participatory approach involving local farmers and the national veterinary services in the control of FMD; and 5) finally the possibility that transfrontier conservation might offer new hope of integrating decision-making at the wildlife-livestock interface
Design and operation of a cryogenic charge-integrating preamplifier for the MuSun experiment
The central detector in the MuSun experiment is a pad-plane time projection
ionization chamber that operates without gas amplification in deuterium at 31
K; it is used to measure the rate of the muon capture process . A new charge-sensitive preamplifier, operated at
140 K, has been developed for this detector. It achieved a resolution of 4.5
keV(D) or 120 RMS with zero detector capacitance at 1.1 s
integration time in laboratory tests. In the experimental environment, the
electronic resolution is 10 keV(D) or 250 RMS at a 0.5 s
integration time. The excellent energy resolution of this amplifier has enabled
discrimination between signals from muon-catalyzed fusion and muon capture on
chemical impurities, which will precisely determine systematic corrections due
to these processes. It is also expected to improve the muon tracking and
determination of the stopping location.Comment: 18 pages + title page, 13 figures, to be submitted to JINST; minor
corrections, added one reference, updated author lis
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