639 research outputs found
Josephson Effect in Pb/I/NbSe2 Scanning Tunneling Microscope Junctions
We have developed a method for the reproducible fabrication of
superconducting scanning tunneling microscope (STM) tips. We use these tips to
form superconductor/insulator/superconductor tunnel junctions with the STM tip
as one of the electrodes. We show that such junctions exhibit fluctuation
dominated Josephson effects, and describe how the Josephson product IcRn can be
inferred from the junctions' tunneling characteristics in this regime. This is
first demonstrated for tunneling into Pb films, and then applied in studies of
single crystals of NbSe2. We find that in NbSe2, IcRn is lower than expected,
which could be attributed to the interplay between superconductivity and the
coexisting charge density wave in this material.Comment: 3 pages, 2 figures. Presented at the New3SC-4 meeting, San Diego,
Jan. 16-21 200
Development and demonstration of manufacturing processes for fabricating graphite/LARC 160 polyimide structural elements
The development and demonstration of manufacturing technologies for the structural application of Celion graphite/LARC-160 polyimide composite material is discussed. Process development and fabrication of demonstration components are discussed. Process development included establishing quality assurance of the basic composite material and processing, nondestructive inspection of fabricated components, developing processes for specific structural forms, and qualification of processes through mechanical testing. Demonstration components were fabricated. The demonstration components consisted of flat laminates, skin/stringer panels, honeycomb panels, chopped fiber compression moldings, and a technology demonstrator segment (TDS) representative of the space shuttle aft body flap
A systematic review of associations between environmental exposures and development of asthma in children aged up to 9 years
Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.Peer reviewedPublisher PD
STM study of multiband superconductivity in NbSe2 using a superconducting tip
We present a method to produce superconducting tips to be used in Scanning
Tunneling Microscopy/Spectroscopy experiments. We use these tips to investigate
the evolution of the electronic density of states of NbSe2 from 0.3K up to its
critical temperature (7.2K). The use of a superconducting tip (Pb) as
ounterelectrode provides an enhancement of the different features related to
the DOS of NbSe2 in the tunneling conductance curves, along all the studied
thermal range. The analysis of the experimental results gives evidence of the
presence of multiband superconductivity in NbSe2.Comment: 5 pages, 5 figures, PDF fil
Coulomb Zero-Bias Anomaly: A Semiclassical Calculation
Effective action is proposed for the problem of Coulomb blocking of
tunneling. The approach is well suited to deal with the ``strong coupling''
situation near zero bias, where perturbation theory diverges. By a
semiclassical treatment, we reduce the physics to that of electrodynamics in
imaginary time, and express the anomaly through exact conductivity of the
system and exact interaction. For the diffusive anomaly, we
compare the result with the perturbation theory of Altshuler, Aronov, and Lee.
For the metal-insulator transition we derive exact relation of the anomaly and
critical exponent of conductivity.Comment: 9 pages, RevTeX 3.
Superconducting Gap and Pseudogap in Iron-Based Layered Superconductor La(OF)FeAs
We report high-resolution photoemission spectroscopy of newly-discovered
iron-based layered superconductor La(OF)FeAs (Tc = 24 K). We
found that the superconducting gap shows a marked deviation from the isotropic
s-wave symmetry. The estimated gap size at 5 K is 3.6 meV in the s- or axial
p-wave case, while it is 4.1 meV in the polar p- or d-wave case. We also found
a pseudogap of 15-20 meV above Tc, which is gradually filled-in with increasing
temperature and closes at temperature far above Tc similarly to copper-oxide
high-temperature superconductors.Comment: 4 pages, 3 figures, J. Phys. Soc. Jpn. Vol. 77, No. 6 (2008), in
pres
Optical transmitter tunable over a 65-nm wavelength range around 1550 nm for quantum key distribution
The ability to create phase-controlled pulses of light with wavelength
tunability has applications spanning quantum and classical communications
networks. Traditionally, optical transmitters are able to either produce
phase-controlled pulses at a fixed wavelength or require a chain of bulky and
expensive external modulators to convert wavelength tunable continuous-wave
light into optical pulses. One technology of great interest is quantum key
distribution (QKD), a technology for generating perfectly random keys at remote
nodes to ensure secure communications. Environments such as data centers, where
the user needs change regularly, will require adaptability in the deployment of
QKD to integrate into classical optical networks. Here we propose and
demonstrate an alternative quantum transmitter design consisting of a
multimodal Fabry-Perot laser optically injection locked by a wavelength tunable
laser. The transmitter is able to produce phase-controlled optical pulses at
GHz speeds with a tunable wavelength range of >65nm centered at 1550 nm. With
this transmitter, we perform proof-of-principle QKD with secure bit rates of
order Mb/s
Electron Quasiparticles Drive the Superconductor-to-Insulator Transition in Homogeneously Disordered Thin Films
Transport data on Bi, MoGe, and PbBi/Ge homogeneously-disordered thin films
demonstrate that the critical resistivity, , at the nominal
insulator-superconductor transition is linearly proportional to the normal
sheet resistance, . In addition, the critical magnetic field scales
linearly with the superconducting energy gap and is well-approximated by
. Because is determined at high temperatures and is the
pair-breaking field, the two immediate consequences are: 1)
electron-quasiparticles populate the insulating side of the transition and 2)
standard phase-only models are incapable of describing the destruction of the
superconducting state. As gapless electronic excitations populate the
insulating state, the universality class is no longer the 3D XY model. The lack
of a unique critical resistance in homogeneously disordered films can be
understood in this context. In light of the recent experiments which observe an
intervening metallic state separating the insulator from the superconductor in
homogeneously disordered MoGe thin films, we argue that the two transitions
that accompany the destruction of superconductivity are 1) superconductor to
Bose metal in which phase coherence is lost and 2) Bose metal to localized
electron insulator via pair-breaking.Comment: This article is included in the Festschrift for Prof. Michael Pollak
on occasion of his 75th birthda
Nanoscale patterning of STIM1 and Orai1 during store-operated Ca2+ entry
Stromal interacting molecule (STIM) and Orai proteins constitute the core machinery of store-operated calcium entry. We used transmission and freeze-fracture electron microscopy to visualize STIM1 and Orai1 at endoplasmic reticulum (ER)-plasma membrane (PM) junctions in HEK 293 cells. Compared with control cells, thin sections of STIM1-transfected cells possessed far more ER elements, which took the form of complex stackable cisternae and labyrinthine structures adjoining the PM at junctional couplings (JCs). JC formation required STIM1 expression but not store depletion, induced here by thapsigargin (TG). Extended molecules, indicative of STIM1, decorated the cytoplasmic surface of ER, bridged a 12-nm ER-PM gap, and showed clear rearrangement into small clusters following TG treatment. Freeze-fracture replicas of the PM of Orai1-transfected cells showed extensive domains packed with characteristic "particles"; TG treatment led to aggregation of these particles into sharply delimited "puncta" positioned upon raised membrane subdomains. The size and spacing of Orai1 channels were consistent with the Orai crystal structure, and stoichiometry was unchanged by store depletion, coexpression with STIM1, or an Orai1 mutation (L273D) affecting STIM1 association. Although the arrangement of Orai1 channels in puncta was substantially unstructured, a portion of channels were spaced at ?15 nm. Monte Carlo analysis supported a nonrandom distribution for a portion of channels spaced at ∼15 nm. These images offer dramatic, direct views of STIM1 aggregation and Orai1 clustering in store-depleted cells and provide evidence for the interaction of a single Orai1 channel with small clusters of STIM1 molecules
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