2,467 research outputs found
The temperature dependence of the local tunnelling conductance in cuprate superconductors with competing AF order
Based on the model with proper chosen parameters for describing
the cuprate superconductors, it is found that near the optimal doping at low
temperature (), only the pure d-wave superconductivity (SC) prevails and
the antiferromagnetic (AF) order is completely suppressed. At higher , the
AF order with stripe modulation and the accompanying charge order may emerge,
and they could exist above the SC transition temperature. We calculate the
local differential tunnelling conductance (LDTC) from the local density of
states (LDOS) and show that their energy variations are rather different from
each other as increases. Although the calculated modulation periodicity in
the LDTC/LDOS and bias energy dependence of the Fourier amplitude of LDTC in
the "pseudogap" region are in good agreement with the recent STM experiment
[Vershinin , Science {\bf 303}, 1995 (2004)], we point out that some of
the energy dependent features in the LDTC do not represent the intrinsic
characteristics of the sample
Anti-phase Modulation of Electron- and Hole-like States in Vortex Core of Bi2Sr2CaCu2Ox Probed by Scanning Tunneling Spectroscopy
In the vortex core of slightly overdoped Bi2Sr2CaCu2Ox, the electron-like and
hole-like states have been found to exhibit spatial modulations in anti-phase
with each other along the Cu-O bonding direction. Some kind of
one-dimensionality has been observed in the vortex core, and it is more clearly
seen in differential conductance maps at lower biases below +-9 mV
STM/STS Study on 4a X 4a Electronic Charge Order of Superconducting Bi2Sr2CaCu2O8+d
We performed low-bias STM measurements on underdoped Bi2212 crystals, and
confirmed that a two-dimensional (2D) superstructure with a periodicity of four
lattice constants (4a) is formed within the Cu-O plane at T<Tc. This 4a X 4a
superstructure, oriented along the Cu-O bonding direction, is nondispersive and
more intense in lightly doped samples with a zero temperature pseudogap (ZTPG)
than in samples with a d-wave gap. The nondispersive 4a X 4a superstructure was
clearly observed within the ZTPG or d-wave gap, while it tended to fade out
outside the gaps. The present results provide a useful test for various models
proposed for an electronic order hidden in the underdoped region of high-Tc
cuprates.Comment: 4 pages, submitted to J. Phys. Soc. Jp
Balloon-borne radiometer measurement of Northern Hemisphere mid-latitude stratospheric HNO3 profiles spanning 12 years
Low-resolution atmospheric thermal emission spectra collected by balloon-borne radiometers over the time span of 1990–2002 are used to retrieve vertical profiles of HNO3, CFC-11 and CFC-12 volume mixing ratios between approximately 10 and 35 km altitude. All of the data analyzed have been collected from launches from a Northern Hemisphere mid-latitude site, during late summer, when stratospheric dynamic variability is at a minimum. The retrieval technique incorporates detailed forward modeling of the instrument and the radiative properties of the atmosphere, and obtains a best fit between modeled and measured spectra through a combination of onion-peeling and global optimization steps. The retrieved HNO3 profiles are consistent over the 12-year period, and are consistent with recent measurements by the Atmospheric Chemistry Experiment-Fourier transform spectrometer satellite instrument. This suggests that, to within the errors of the 1990 measurements, there has been no significant change in the HNO3 summer mid-latitude profile
Prevalence of mixed genotype hepatitis C virus infections in the UK as determined by genotype‐specific PCR and deep sequencing
The incidence of mixed genotype hepatitis C virus infections in the UK is largely unknown. As the efficacy of direct acting antivirals is variable across different genotypes, treatment regimens are tailored to the infecting genotype, which may pose issues for the treatment of underlying genotypes within undiagnosed mixed genotype HCV infections. There is therefore a need to accurately diagnose mixed genotype infections prior to treatment. PCR-based diagnostic tools were developed to screen for the occurrence of mixed genotype infections caused by the most common UK genotypes, 1a and 3, in a cohort of 506 individuals diagnosed with either of these genotypes. The overall prevalence rate of mixed infection was 3.8% however this rate was unevenly distributed, with 6.7% of individuals diagnosed with genotype 3 harbouring genotype 1a strains and only 0.8% of samples from genotype 1a patients harbouring genotype 3 (p<0.05). Mixed infection samples consisted of a major and a minor genotype, with the latter constituting less than 21% of the total viral load and, in 67% of cases, less than 1% of the viral load. Analysis of a subset of the cohort by Illumina PCR-next generation sequencing resulted in a much greater incidence rate than obtained by PCR. This may have occurred due to the non-quantitative nature of the technique and despite the designation of false positive thresholds based on negative controls
Evolution of the electronic excitation spectrum with strongly diminishing hole-density in superconducting Bi_{2}Sr_{2}CaCu_{2}O_{8+\delta}
A complete knowledge of its excitation spectrum could greatly benefit efforts
to understand the unusual form of superconductivity occurring in the lightly
hole-doped copper-oxides. Here we use tunnelling spectroscopy to measure the
T\to 0 spectrum of electronic excitations N(E) over a wide range of
hole-density p in superconducting Bi_{2}Sr_{2}CaCu_{2}O_{8+/delta}. We
introduce a parameterization for N(E) based upon an anisotropic energy-gap
/Delta (\vec k)=/Delta_{1}(Cos(k_{x})-Cos(k_{y}))/2 plus an effective
scattering rate which varies linearly with energy /Gamma_{2}(E) . We
demonstrate that this form of N(E) allows successful fitting of differential
tunnelling conductance spectra throughout much of the
Bi_{2}Sr_{2}CaCu_{2}O_{8+/delta} phase diagram. The resulting average
/Delta_{1} values rise with falling p along the familiar trajectory of
excitations to the 'pseudogap' energy, while the key scattering rate
/Gamma_{2}^{*}=/Gamma_{2}(E=/Delta_{1}) increases from below ~1meV to a value
approaching 25meV as the system is underdoped from p~16% to p<10%. Thus, a
single, particle-hole symmetric, anisotropic energy-gap, in combination with a
strongly energy and doping dependent effective scattering rate, can describe
the spectra without recourse to another ordered state. Nevertheless we also
observe two distinct and diverging energy scales in the system: the energy-gap
maximum /Delta_{1} and a lower energy scale /Delta_{0} separating the spatially
homogeneous and heterogeneous electronic structures.Comment: High resolution version available at:
http://people.ccmr.cornell.edu/~jcdavis/files/Alldredge-condmat08010087-highres.pd
A momentum-dependent perspective on quasiparticle interference in Bi_{2}Sr_{2}CaCu_{2}O_{8+\delta}
Angle Resolved Photoemission Spectroscopy (ARPES) probes the momentum-space
electronic structure of materials, and provides invaluable information about
the high-temperature superconducting cuprates. Likewise, the cuprate
real-space, inhomogeneous electronic structure is elucidated by Scanning
Tunneling Spectroscopy (STS). Recently, STS has exploited quasiparticle
interference (QPI) - wave-like electrons scattering off impurities to produce
periodic interference patterns - to infer properties of the QP in
momentum-space. Surprisingly, some interference peaks in
Bi_{2}Sr_{2}CaCu_{2}O_{8+\delta} (Bi-2212) are absent beyond the
antiferromagnetic (AF) zone boundary, implying the dominance of particular
scattering process. Here, we show that ARPES sees no evidence of quasiparticle
(QP) extinction: QP-like peaks are measured everywhere on the Fermi surface,
evolving smoothly across the AF zone boundary. This apparent contradiction
stems from different natures of single-particle (ARPES) and two-particle (STS)
processes underlying these probes. Using a simple model, we demonstrate
extinction of QPI without implying the loss of QP beyond the AF zone boundary
Local edge modes in doped cuprates with checkerboard polaronic heterogeneity
We study a periodic polaronic system, which exhibits a nanoscale superlattice
structure, as a model for hole-doped cuprates with checkerboard-like
heterogeneity, as has been observed recently by scanning tunneling microscopy
(STM). Within this model, the electronic and phononic excitations are
investigated by applying an unrestricted Hartree-Fock and a random phase
approximation (RPA) to a multiband Peierls-Hubbard Hamiltonian in two
dimensions
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