6,638 research outputs found
Localized electronic states and photoemission superconducting condensate in BiSrCaCuO
We present the first detailed angle-resolved photoemission evidence that
there are two types of carriers that contribute to the photoemission
superconducting condensate in . Our data
indicate that both itinerant and somewhat localized normal state carriers can
contribute to the formation of Cooper pairs.Comment: APS_Revtex, 11 pages, including 3 figures, available upon request.
UW-Madison preprint#
Temperature dependence of the superconducting gap anisotropy in BiSrCaCuO
We present the first detailed data of the momentum-resolved, temperature
dependence of the superconducting gap of ,
complemented by similar data on the intensity of the photoemission
superconducting condensate spectral area. The gap anisotropy between the
and directions increases markedly with increasing
temperature, contrary to what happens for conventional anisotropic-gap
superconductors such as lead. Specifically, the size of the superconducting gap
along the direction decreases to values indistinguishable from zero
at temperatures for which the gap retains virtually full value along the
direction.Comment: APS_REVTEX. 19 pages, including 8 figures, available upon request.
UW-Madison preprin
Localization Effects in Bi2Sr2Ca(Cu,Co)2O8+y High Temperature Superconductors
Doping Bi2Sr2Ca1Cu2O8+y with Co causes a superconductor-insulator transition.
We study correlations between changes in the electrical resistivity RHOab(T)
and the electronic bandstructure using identical single crystalline samples.
For undoped samples the resistivity is linear in temperature and has a
vanishing residual resistivity. In angle resolved photoemission these samples
show dispersing band-like states. Co-doping decreases TC and causes and
increase in the residual resistivity. Above a threshold Co-concentration the
resistivity is metallic (drab/dT >0) at room temperature, turns insulating
below a characteristic temperature Tmin and becomes super- conducting at even
lower temperature. These changes in the resistivity correlate with the
disappearance of the dispersing band-like states in angle resolved
photoemission. We show that Anderson localization caused by the impurity
potential of the doped Co-atoms provides a consistent explanation of all
experimental features. Therefore the TC reduction in 3d-metal doped high-
temperature superconductors is not caused by Abrikosov Gor'kov pair- breaking
but by spatial localization of the carriers. The observed suppression of TC
indicates that the system is in the homogenous limit of the
superconductor-insulator transition. The coexistance of insulating (dRHOab/dT
<0) normal state behavior and super- conductivity indicates that the
superconducting ground state is formed out of spatially almost localized
carriers.Comment: Postscript file 11 pages plus 4 figures available on reques
Observation of a van Hove Singularity in with Angle Resolved Photoemission
We have performed high energy resolution angle-resolved photoemission studies
of the normal state band structure of oxygen overdoped
. We find that there is an extended saddle
point singularity in the density of states along direction.
The data also indicate that there is an asymmetry in the Fermi surface for both
the and perpendicular directions.Comment: APS_Revtex. 28 pages, including 16 figures, available upon request.
UW-Madison preprint#
Probing Fine-Scale Ionospheric Structure with the Very Large Array Radio Telescope
High resolution (~1 arcminute) astronomical imaging at low frequency (below
150 MHz) has only recently become practical with the development of new
calibration algorithms for removing ionospheric distortions. In addition to
opening a new window in observational astronomy, the process of calibrating the
ionospheric distortions also probes ionospheric structure in an unprecedented
way. Here we explore one aspect of this new type of ionospheric measurement,
the differential refraction of celestial source pairs as a function of their
angular separation. This measurement probes variations in the spatial gradient
of the line-of-sight total electron content (TEC) to 0.001 TECU/km accuracy
over spatial scales of under 10 km to over 100 km. We use data from the VLA
Low-frequency Sky Survey (VLSS; Cohen et al. 2007, AJ 134, 1245), a nearly
complete 74 MHz survey of the entire sky visible to the Very Large Array (VLA)
telescope in Socorro, New Mexico. These data comprise over 500 hours of
observations, all calibrated in a standard way. While ionospheric spatial
structure varies greatly from one observation to the next, when analyzed over
hundreds of hours, statistical patterns become apparent. We present a detailed
characterization of how the median differential refraction depends on source
pair separation, elevation and time of day. We find that elevation effects are
large, but geometrically predictable and can be "removed" analytically using a
"thin-shell" model of the ionosphere. We find significantly greater ionospheric
spatial variations during the day than at night. These diurnal variations
appear to affect the larger angular scales to a greater degree indicating that
they come from disturbances on relatively larger spatial scales (100s of km,
rather than 10s of km).Comment: Accepted for publication by The Astronomical Journa
Effect of Iodine Doping on BiSrCaCuO: Charge Transfer or Interlayer Coupling?
A comparative study has been made of iodine-intercalated
BiSrCaCuO single crystal and 1 atm O
annealed BiSrCaCuO single crystal using AC
susceptibility measurement, X-ray photoemission (XPS) and angle-resolved
ultraviolet photoemission spectroscopy (ARUPS). AC susceptibility measurement
indicates that O-doped samples studied have T of 84 K,
whereas T of Iodine-doped samples studied are 80 K. XPS Cu 2p core
level data establish that the hole concentration in the CuO planes are
essentially the same for these two kinds of samples. ARUPS measurements show
that electronic structure of the normal states near the Fermi level has been
strongly affected by iodine intercalation. We conclude that the dominant effect
of iodine doping is to alter the interlayer coupling.Comment: LBL 9 pages, APS_Revtex. 5 Figures, available upon request.
UW-Madison preprin
Higher anisotropic d-wave symmetry in cuprate superconductors
We derive a pair potential from tight binding further neighbours attraction
that leads to superconducting gap symmetry similar to that of the
phenomenological spin fluctuation theory of high temperature superconductors
(Monthoux, Balatsky, Pines, Phys. Rev. Lett. {\bf 67}, 3448). We show that
higher anisotropic d-wave than the simpliest d-wave symmetry is one of the
important ingredients responsible for higher BCS characteristic ratio.Comment: Latex 5 pages, 3 figures attached, Journal Ref. : Journal of Physics
C, Vol. 11, issue 30, L371-L377 (1999
A Pathogen Secreted Protein as a Detection Marker for Citrus Huanglongbing.
The citrus industry is facing an unprecedented crisis due to Huanglongbing (HLB, aka citrus greening disease), a bacterial disease associated with the pathogen Candidatus Liberibacter asiaticus (CLas) that affects all commercial varieties. Transmitted by the Asian citrus psyllid (ACP), CLas colonizes citrus phloem, leading to reduced yield and fruit quality, and eventually tree decline and death. Since adequate curative measures are not available, a key step in HLB management is to restrict the spread of the disease by identifying infected trees and removing them in a timely manner. However, uneven distribution of CLas cells in infected trees and the long latency for disease symptom development makes sampling of trees for CLas detection challenging. Here, we report that a CLas secreted protein can be used as a biomarker for detecting HLB infected citrus. Proteins secreted from CLas cells can presumably move along the phloem, beyond the site of ACP inoculation and CLas colonized plant cells, thereby increasing the chance of detecting infected trees. We generated a polyclonal antibody that effectively binds to the secreted protein and developed serological assays that can successfully detect CLas infection. This work demonstrates that antibody-based diagnosis using a CLas secreted protein as the detection marker for infected trees offers a high-throughput and economic approach that complements the approved quantitative polymerase chain reaction-based methods to enhance HLB management programs
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