395 research outputs found
Admixtures to d-wave gap symmetry in untwinned YBa2Cu3O7 superconducting films measured by angle-resolved electron tunneling
We report on an \textit{ab}-anisotropy of and in
ramp-edge junctions between untwinned YBaCuO and % -wave
Nb. For these junctions, the angle with the YBaCuO
crystal b-axis is varied as a single parameter. The
A()-dependence presents 2-fold symmetry. The minima in
at suggest a real s-wave subdominant
component and negligible -wave or imaginary s-wave admixtures. The
()-dependence is well-fitted by 83% -, 15%
isotropic - and 2% anisotropic s-wave order parameter symmetry, consistent
with .Comment: 4 pages, 3 figures, to be published in Physical Review Letter
Observation of Andreev bound states in YBaCuO/Au/Nb ramp-type Josephson junctions
We report on Josephson and quasiparticle tunneling in YBa2Cu3O7-x(YBCO)/Au/Nb
ramp junctions of several geometries. Macroscopically, tunneling occurs in the
ab-plane of YBCO either in the (100) and (010) direction, or in the (110)
direction. These junctions have a stable and macroscopically well defined
geometry. This allows systematic investigations of both quasiparticle and
Josephson tunneling over a wide range of temperature and magnetic field. With
Nb superconducting, its gap appears in the quasiparticle conductance spectra as
Nb coherence peaks and a dip at the center of a broadened zero-bias conductance
peak (ZBCP). As we increase the temperature or an applied magnetic field both
the Nb coherence peaks and the dip get suppressed and the ZBCP fully develops,
while states are conserved. With Nb in the normal state the ZBCP is observed up
to about 77 K and is almost unaffected by an increasing field up to 7 T. The
measurements are consistent with a convolution of density of states with
broadened Andreev bound states formed at the YBCO/Au/Nb junction interfaces.
Since junctions with different geometries are fabricated on the same substrate
under the same conditions one expects to extract reliable tunneling information
that is crystallographic direction sensitive. In high contrast to Josephson
tunneling, however, the quasiparticle conductance spectra are crystallographic
orientation insensitive: independent whether the tunneling occurs in the (100)
or (110) directions, a pronounced ZBCP is always observed, consistent with
microscopic roughness of the junction interfaces. Qualitatively, all these
particularities regarding quasiparticle spectra hold regardless whether the
YBCO thin film is twinned or untwinned.Comment: 13 pages, 10 figure
Anti-ferromagnetic ordering in arrays of superconducting pi-rings
We report experiments in which one dimensional (1D) and two dimensional (2D)
arrays of YBa2Cu3O7-x-Nb pi-rings are cooled through the superconducting
transition temperature of the Nb in various magnetic fields. These pi-rings
have degenerate ground states with either clockwise or counter-clockwise
spontaneous circulating supercurrents. The final flux state of each ring in the
arrays was determined using scanning SQUID microscopy. In the 1D arrays,
fabricated as a single junction with facets alternating between alignment
parallel to a [100] axis of the YBCO and rotated 90 degrees to that axis,
half-fluxon Josephson vortices order strongly into an arrangement with
alternating signs of their magnetic flux. We demonstrate that this ordering is
driven by phase coupling and model the cooling process with a numerical
solution of the Sine-Gordon equation. The 2D ring arrays couple to each other
through the magnetic flux generated by the spontaneous supercurrents. Using
pi-rings for the 2D flux coupling experiments eliminates one source of disorder
seen in similar experiments using conventional superconducting rings, since
pi-rings have doubly degenerate ground states in the absence of an applied
field. Although anti-ferromagnetic ordering occurs, with larger negative bond
orders than previously reported for arrays of conventional rings, long-range
order is never observed, even in geometries without geometric frustration. This
may be due to dynamical effects. Monte-Carlo simulations of the 2D array
cooling process are presented and compared with experiment.Comment: 10 pages, 15 figure
Ground state and bias current induced rearrangement of semifluxons in 0-pi long Josephson junctions
We investigate numerically a long Josephson junction with several phase
pi-discontinuity points. Such junctions are usually fabricated as a ramp
between an anisotropic cuprate superconductor like YBCO and an isotropic metal
superconductor like Nb. From the top, they look like zigzags with pi-jumps of
the Josephson phase at the corners. These pi-jumps, at certain conditions, lead
to the formation of half-integer flux quanta, which we call semifluxons (SF),
pinned at the corners. We show (a) that the spontaneous formation of SFs
depends on the junction length, (b) that the ground state without SFs can be
converted to a state with SFs by applying a bias current, (c) that the SF
configuration can be rearranged by the bias current. All these effects can be
observed using a SQUID microscope.Comment: ~8 pages, 6 figures, submitted to PR
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
Whole-genome sequencing analysis reveals the spread of a vanB-carrying transposon among different vancomycin-resistant Enterococcus faecium clinical isolates in a non-endemic setting
Background: Vancomycin-resistant enterococci (VRE), particularly Enterococcus faecium (VREfm), can cause serious nosocomial infections, and have been responsible for healthcare-associated outbreaks. Spreading of VREfm can occur both clonally and by the dissemination of mobile genetic elements. Aim: To report prospective analysis of whole-genome sequencing (WGS) data, including both core-genome multi-locus sequence typing (cgMLST) and transposon analysis, during a vanB VREfm outbreak. Methods: Screening for vanB-positive VREfm isolates was performed by real-time polymerase chain reaction (PCR) on an overnight enriched broth and, if positive, subculture was performed. vanB-positive VREfm isolates underwent WGS. Generated data were used for molecular typing that was performed by cgMLST using SeqSphere. For transposon characterization, sequence data were mapped against the reference sequence of transposon Tn1549 using CLC Genomics Workbench, or de-novo assemblies were used for BLASTN comparisons. Results: In total, 1358 real-time PCRs were performed. Two hundred and fifty-one specimens from 207 patients tested positive on PCR for vanB, of which 13 specimens obtained from six patients were identified as vanB VREfm positive on culture. These six patients harboured seven unique isolates belonging to four cluster types: CT118 (N=2), CT2483 (N=3), CT2500 (N=1) and CT2501 (N=1). Transposon analysis revealed the presence of an identical vanB-carrying transposon in the isolates cultured from all six patientsBackground: Vancomycin-resistant enterococci (VRE), particularly Enterococcus faecium (VREfm), can cause serious nosocomial infections, and have been responsible for healthcare-associated outbreaks. Spreading of VREfm can occur both clonally and by the dissemination of mobile genetic elements.Aim: To report prospective analysis of whole-genome sequencing (WGS) data, including both core-genome multi-locus sequence typing (cgMLST) and transposon analysis, during a vanB VREfm outbreak.Methods: Screening for vanB-positive VREfm isolates was performed by real-time polymerase chain reaction (PCR) on an overnight enriched broth and, if positive, subculture was performed. vanB-positive VREfm isolates underwent WGS. Generated data were used for molecular typing that was performed by cgMLST using SeqSphere. For transposon characterization, sequence data were mapped against the reference sequence of transposon Tn1549 using CLC Genomics Workbench, or de-novo assemblies were used for BLASTN comparisons.Results: In total, 1358 real-time PCRs were performed. Two hundred and fifty-one specimens from 207 patients tested positive on PCR for vanB, of which 13 specimens obtained from six patients were identified as vanB VREfm positive on culture. These six patients harboured seven unique isolates belonging to four cluster types: CT118 (N=2), CT2483 (N=3), CT2500 (N=1) and CT2501 (N=1). Transposon analysis revealed the presence of an identical vanB-carrying transposon in the isolates cultured from all six patients that could be linked based on epidemiological data.Conclusion: A vanB VREfm outbreak occurred in the study hospital, including six patients with isolates belonging to four cluster types. In-depth transposon analysis revealed that & nbsp;dissemination of transposon Tn1549 rather than clonal spread was the cause of the outbreak.(C)& nbsp;2021 The Healthcare Infection Society. Published by Elsevier Ltd. All rights reserved.</p
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