200 research outputs found
A Cross-Whiskers Junction as a Novel Fabrication Process for Intrinsic Josephson Junction
A Bi2Sr2CaCu2O8+d cross-whiskers junction has been successfully discovered as
a novel intrinsic Josephson junction without using any technique for
micro-fabrication. Two Bi2Sr2CaCu2O8+d whisker crystals were placed crosswise
on a MgO substrate and heated at 850C for 30 min. They were electrically
connected at their c-planes. The measurement terminals were made at the four
ends of the whiskers. The I-V characteristics of the cross-whiskers junction at
5K were found to show a clear multiple-branch structure with a spacing of
approximately 15 mV that is a feature of the intrinsic Josephson junction. The
critical current density Jc was estimated to be 1170 A/cm2. The
branch-structure was strongly suppressed by the magnetic field above 1kOe.Comment: 4 pages, PDF fil
d-like Symmetry of the Order Parameter and Intrinsic Josephson Effects in Bi2212 Cross-Whisker Junctions
An intrinsic tunnel junction was made using two Bi-2212 single crystal
whiskers. The two whiskers with a cross-angle were overlaid at their c-planes
and connected by annealing. The angular dependence of the critical current
density along the c-axis is of the d-wave symmetry. However, the angular
dependence is much stronger than that of the conventional d-wave. Furthermore,
the current vs. voltage characteristics of the cross-whiskers junctions show a
multiple-branch structure at any cross-angle, indicating the formation of the
intrinsic Josephson junction array.Comment: 4 pages PDF fil
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Femtosecond spectroscopy in a nearly optimally doped Fe-based superconductors FeSe0.5Te0.5 and Ba(Fe 1-xCox)2As2/Fe thin film
Femtosecond spectroscopy has been used to investigate the quasi-particle relaxation times in nearly optimally doped Fe-based superconductors FeSe 0.5Te0.5 and optimally doped Ba-122 thin films growth on a Fe buffer layer. Experimental results concerning the temperature dependence of the relaxation time of such pnictides both in the superconducting state are now presented and discussed. Modelling the T-dependence of relaxation times an estimation of both electron-phonon constant and superconducting energy gap in the excitation spectrum of both Fe(Se,Te) and Ba-122 compounds is obtained
Elemental characterisation of melanin in feathers via synchrotron X-ray imaging and absorption spectroscopy
Melanin is a critical component of biological systems, but the exact chemistry of melanin is still imprecisely known. This is partly due to melanin’s complex heterogeneous nature and partly because many studies use synthetic analogues and/or pigments extracted from their natural biological setting, which may display important differences from endogenous pigments. Here we demonstrate how synchrotron X-ray analyses can non-destructively characterise the elements associated with melanin pigment in situ within extant feathers. Elemental imaging shows that the distributions of Ca, Cu and Zn are almost exclusively controlled by melanin pigment distribution. X-ray absorption spectroscopy demonstrates that the atomic coordination of zinc and sulfur is different within eumelanised regions compared to pheomelanised regions. This not only impacts our fundamental understanding of pigmentation in extant organisms but also provides a significant contribution to the evidence-based colour palette available for reconstructing the appearance of fossil organisms
Branching Ratio and CP Violation of B to pi pi Decays in Perturbative QCD Approach
We calculate the branching ratios and CP asymmetries for B^0 to pi^+pi^-, B^+
to pi^+pi^0 and B^0 to pi^0pi^0 decays, in a perturbative QCD approach. In this
approach, we calculate non-factorizable and annihilation type contributions, in
addition to the usual factorizable contributions. We found that the
annihilation diagram contributions are not very small as previous argument. Our
result is in agreement with the measured branching ratio of B to pi^+pi^- by
CLEO collaboration. With a non-negligible contribution from annihilation
diagrams and a large strong phase, we predict a large direct CP asymmetry in
B^0 to pi^+pi^-, and pi^0pi^0, which can be tested by the current running B
factories.Comment: Latex, 28 pages including 11 figures; added contents and figures,
corrected typo
Signatures of valence fluctuations in CeCu2Si2 under high pressure
Simultaneous resistivity and a.c.-specific heat measurements have been
performed under pressure on single crystalline CeCu2Si2 to over 6 GPa in a
hydrostatic helium pressure medium. A series of anomalies were observed around
the pressure coinciding with a maximum in the superconducting critical
temperature, . These anomalies can be linked with an abrupt change
of the Ce valence, and suggest a second quantum critical point at a pressure
GPa, where critical valence fluctuations provide the
superconducting pairing mechanism, as opposed to spin fluctuations at ambient
pressure. Such a valence instability, and associated superconductivity, is
predicted by an extended Anderson lattice model with Coulomb repulsion between
the conduction and f-electrons. We explain the T-linear resistivity found at
in this picture, while other anomalies found around can be
qualitatively understood using the same model.Comment: Submitted to Phys. Rev.
Probe of bending motion following the 1s[–1]π* excitation of N2O
The doubly degenerate core-excitedΠstate of N2O splits into two due to the static Renner–Teller effect. The lower state, A1, has a bent stable geometry and the molecule excited to this state starts to deform itself toward this bent geometry. To probe the effect of the potential energy surfaces of the core-excited A1 states on the nuclear motion, we measure the momenta of the three atomic ions in coincidence by means of the ion momentum imaging technique. We find that the potential energy surface affects the molecular deformation significantly. N2O in the terminal N 1s[–1]3πA1 excited state is observed to be bent more than that in the central N 1s[–1]3πA1 excited state. This means that N2O in the terminal N 1s[–1]3πA1 excited state bends faster than that in the central N 1s[–1]3πA1 excited state. When the excitation energy is decreased within the 1s[–1]3π resonances, the nuclear motion in the A1 states becomes faster. This is interpreted by the notion that the excitation occurs onto the steeper slope part of the potential energy surface of the excited state for the lower excitation energy. The branching ratio of the A1 excitation increases with the decrease in the excitation energy. ©2004 American Institute of Physics
Synchrotron X-ray absorption spectroscopy of melanosomes in vertebrates and cephalopods: implications for the affinity of Tullimonstrum
Screening pigments are essential for vision in animals. Vertebrates use melanins bound in melanosomes as screening pigments, whereas cephalopods are assumed to use ommochromes. Preserved eye melanosomes in the controversial fossil Tullimonstrum (Mazon Creek, IL, USA) are partitioned by size and/or shape into distinct layers. These layers resemble tissue-specific melanosome populations considered unique to the vertebrate eye. Here, we show that extant cephalopod eyes also show tissue-specific size- and/or shape-specific partitioning of melanosomes; these differ from vertebrate melanosomes in the relative abundance of trace metals and in the binding environment of copper. Chemical signatures of melanosomes in the eyes of Tullimonstrum more closely resemble those of modern cephalopods than those of vertebrates, suggesting that an invertebrate affinity for Tullimonstrum is plausible. Melanosome chemistry may thus provide insights into the phylogenetic affinities of enigmatic fossils where melanosome size and/or shape are equivocal
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