205 research outputs found
Dynamical effects of an unconventional current-phase relation in YBCO dc-SQUIDs
The predominant d-wave pairing symmetry in high temperature superconductors
allows for a variety of current-phase relations in Josephson junctions, which
is to a certain degree fabrication controlled. In this letter we report on
direct experimental observations of the effects of a non-sinusoidal
current-phase dependence in YBCO dc-SQUIDs, which agree with the theoretical
description of the system.Comment: 4 pages, 4 ps figures, to apprear in Phys. Rev. Let
Modifying the surface electronic properties of YBa2Cu3O7-delta with cryogenic scanning probe microscopy
We report the results of a cryogenic study of the modification of
YBa2Cu3O7-delta surface electronic properties with the probe of a scanning
tunneling microscope (STM). A negative voltage applied to the sample during STM
tunneling is found to modify locally the conductance of the native degraded
surface layer. When the degraded layer is removed by etching, the effect
disappears. An additional surface effect is identified using Scanning Kelvin
Probe Microscopy in combination with STM. We observe reversible surface
charging for both etched and unetched samples, indicating the presence of a
defect layer even on a surface never exposed to air.Comment: 6 pages, 4 figures. To appear in Superconductor Science and
Technolog
Shot noise in normal metal-d-wave superconducting junctions
We present theoretical calculations and predictions for the shot noise in
voltage biased junctions of superconductors and normal metal
counter-electrodes. In the clean limit for the d-wave superconductor the shot
noise vanishes at zero voltage because of resonant Andreev reflection by
zero-energy surface bound states. We examine the sensitivity of this resonance
to impurity scattering. We report theoretical results for the magnetic field
dependence of the shot noise, as well the fingerprints of subdominant - and
pairing channels.Comment: 15 pages, 8 figures and 3 tables embedde
Evaluation of a calibration rig for stereo laparoscopes
BACKGROUND: Accurate camera and hand-eye calibration are essential to ensure high quality results in image guided surgery applications. The process must also be able to be undertaken by a non-expert user in a surgical setting. PURPOSE: This work seeks to identify a suitable method for tracked stereo laparoscope calibration within theatre. METHODS: A custom calibration rig, to enable rapid calibration in a surgical setting, was designed. The rig was compared against freehand calibration. Stereo reprojection, stereo reconstruction, tracked stereo reprojection and tracked stereo reconstruction error metrics were used to evaluate calibration quality. RESULTS: Use of the calibration rig reduced mean errors: reprojection (1.47mm [SD 0.13] vs 3.14mm [SD 2.11], p-value 1e-8), reconstruction (1.37px [SD 0.10] vs 10.10px [SD 4.54], p-value 6e-7) and tracked reconstruction (1.38mm [SD 0.10] vs 12.64mm [SD 4.34], p-value 1e-6) compared with freehand calibration. The use of a ChArUco pattern yielded slightly lower reprojection errors, while a dot grid produced lower reconstruction errors and was more robust under strong global illumination. CONCLUSION: The use of the calibration rig results in a statistically significant decrease in calibration error metrics, versus freehand calibration, and represents the preferred approach for use in the operating theatre. This article is protected by copyright. All rights reserved
Quantum Optics and Photonics
Contains reports on five research projects.Joint Services Electronics Program (Contract DAALO3-86-K-0002)National Science Foundation (Grant PHY 82-10369)U.S. Air Force - Office of Scientific Research (Contract F49620-82-C-0091)U.S. Air Force - Rome Air Development Cente
Influence of impurity-scattering on tunneling conductance in d-wave superconductors with broken time reversal symmetry
Effects of impurity scattering on tunneling conductance in dirty
normal-metal/insulator/superconductor junctions are studied based on the Kubo
formula and the recursive Green function method. The zero-bias conductance peak
(ZBCP) is a consequence of the unconventional pairing symmetry in
superconductors. The impurity scattering in normal metals suppresses the
amplitude of the ZBCP. The degree of the suppression agrees well with results
of the quasiclassical Green function theory. When superconductors have
+is-wave pairing symmetry, the time-reversal symmetry is broken in
superconductors and the ZBCP splits into two peaks. The random impurity
scattering reduces the height of the two splitting peaks. The position of the
splitting peaks, however, almost remains unchanged even in the presence of the
strong impurity scattering. Thus the two splitting peaks never merge into a
single ZBCP.Comment: 12 pages, 5 figures, using jpsj2.cls and overcite.st
Project overview and update on WEAVE: the next generation wide-field spectroscopy facility for the William Herschel Telescope
We present an overview of and status report on the WEAVE next-generation
spectroscopy facility for the William Herschel Telescope (WHT). WEAVE
principally targets optical ground-based follow up of upcoming ground-based
(LOFAR) and space-based (Gaia) surveys. WEAVE is a multi-object and multi-IFU
facility utilizing a new 2-degree prime focus field of view at the WHT, with a
buffered pick-and-place positioner system hosting 1000 multi-object (MOS)
fibres, 20 integral field units, or a single large IFU for each observation.
The fibres are fed to a single spectrograph, with a pair of 8k(spectral) x 6k
(spatial) pixel cameras, located within the WHT GHRIL enclosure on the
telescope Nasmyth platform, supporting observations at R~5000 over the full
370-1000nm wavelength range in a single exposure, or a high resolution mode
with limited coverage in each arm at R~20000. The project is now in the final
design and early procurement phase, with commissioning at the telescope
expected in 2017.Comment: 11 pages, 11 Figures, Summary of a presentation to Astronomical
Telescopes and Instrumentation 201
Josephson effect in d-wave superconductor junctions in a lattice model
Josephson current between two d-wave superconductors is calculated by using a
lattice model. Here we consider two types of junctions, , the parallel
junction and the mirror-type junction. The maximum Josephson current
shows a wide variety of temperature () dependence depending on the
misorientation angles and the types of junctions. When the misorientation
angles are not zero, the Josephson current shows the low-temperature anomaly
because of a zero energy state (ZES) at the interfaces. In the case of
mirror-type junctions, has a non monotonic temperature dependence. These
results are consistent with the previous results based on the quasiclassical
theory. [Y. Tanaka and S. Kashiwaya: Phys. Rev. B \textbf{56} (1997) 892.] On
the other hand, we find that the ZES disappears in several junctions because of
the Freidel oscillations of the wave function, which is peculiar to the lattice
model. In such junctions, the temperature dependence of is close to the
Ambegaokar-Baratoff relation.Comment: 17 pages, 10 figures, using jpsj2.cls and oversite.st
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