266 research outputs found
Linear response and collective oscillations in superconductors with d-wave pairing
Simple and physically transparent equations for the linear response of
layered superconductors with d-wave symmetry of the order parameter are derived
by means of the quasiclassic kinetic theory of superconductivity. Responses to
solenoidal and potential electric fields have different frequency dependencies.
The conductivity describing the response to the solenoidal field is limited by
the momentum relaxation, like in a normal metal. The response to the potential
electric field depends, in addition, on the branch imbalance relaxation rate.
The damping of plasma oscillations of superconducting electrons is determined
by dielectric relaxation and is small. Relaxation of branch imbalance
determined by elastic scattering is large enough to make the Carlson-Goldman
mode in d-wave superconductors overdamped.Comment: 11 pages, latex, no figures, submitted to Physical Review
Definitive experimental evidence for two-band superconductivity in MgB2
The superconducting gap of MgB2 has been studied by high-resolution
angle-resolved photoemission spectroscopy (ARPES). The momentum(k)-resolving
capability of ARPES enables us to identify the s- and p-orbital derived bands
predicted from band structure calculations and to successfully measure the
superconducting gap on each band. The results show that superconducting gaps
with values of 5.5 meV and 2.2 meV open on the s-band and the p-band,
respectively, but both the gaps close at the bulk transition temperature,
providing a definitive experimental evidence for the two-band superconductivity
in MgB2. The experiments validate the role of k-dependent electron-phonon
coupling as the origin of multiple-gap superconductivity in MgB2.Comment: PDF file onl
Open Data for Global Multimodal Land Use Classification: Outcome of the 2017 IEEE GRSS Data Fusion Contest
In this paper, we present the scientific outcomes of the 2017 Data Fusion Contest organized by the Image Analysis and Data Fusion Technical Committee of the IEEE Geoscience and Remote Sensing Society. The 2017 Contest was aimed at addressing the problem of local climate zones classification based on a multitemporal and multimodal dataset, including image (Landsat 8 and Sentinel-2) and vector data (from OpenStreetMap). The competition, based on separate geographical locations for the training and testing of the proposed solution, aimed at models that were accurate (assessed by accuracy metrics on an undisclosed reference for the test cities), general (assessed by spreading the test cities across the globe), and computationally feasible (assessed by having a test phase of limited time). The techniques proposed by the participants to the Contest spanned across a rather broad range of topics, and of mixed ideas and methodologies deriving from computer vision and machine learning but also deeply rooted in the specificities of remote sensing. In particular, rigorous atmospheric correction, the use of multidate images, and the use of ensemble methods fusing results obtained from different data sources/time instants made the difference
Magnetic field dependence of superconducting energy gaps in YNi2B2C: Evidence of multiband superconductivity
We present results of in field directional point contact spectroscopy (DPCS)
study in the quaternary borocarbide superconductor YNi2B2C, which is
characterized by a highly anisotropic superconducting gap function. For I||a,
the superconducting energy gap (D), decreases linearly with magnetic field and
vanishes around 3.25T which is well below the upper critical field (Hc2~6T)
measured at the same temperature (2.2K). For I||c, on the other hand, D
decreases weakly with magnetic field but the broadening parameter (G) increases
rapidly with magnetic field with the absence of any resolvable feature above
3.5T. From an analysis of the field variation of energy gaps and the zero bias
density of states we show that the unconventional gap function observed in this
material could originate from multiband superconductivity.Comment: 19 pages including figures (final version
Generation of angular-momentum-dominated electron beams from a photoinjector
Various projects under study require an angular-momentum-dominated electron
beam generated by a photoinjector. Some of the proposals directly use the
angular-momentum-dominated beams (e.g. electron cooling of heavy ions), while
others require the beam to be transformed into a flat beam (e.g. possible
electron injectors for light sources and linear colliders). In this paper, we
report our experimental study of an angular-momentum-dominated beam produced in
a photoinjector, addressing the dependencies of angular momentum on initial
conditions. We also briefly discuss the removal of angular momentum. The
results of the experiment, carried out at the Fermilab/NICADD Photoinjector
Laboratory, are found to be in good agreement with theoretical and numerical
models.Comment: 8 pages, 7 figures, submitted to Phys. Rev. ST Accel. Beam
Cross-Attention in Coupled Unmixing Nets for Unsupervised Hyperspectral Super-Resolution
The recent advancement of deep learning techniques has made great progress on
hyperspectral image super-resolution (HSI-SR). Yet the development of
unsupervised deep networks remains challenging for this task. To this end, we
propose a novel coupled unmixing network with a cross-attention mechanism,
CUCaNet for short, to enhance the spatial resolution of HSI by means of
higher-spatial-resolution multispectral image (MSI). Inspired by coupled
spectral unmixing, a two-stream convolutional autoencoder framework is taken as
backbone to jointly decompose MS and HS data into a spectrally meaningful basis
and corresponding coefficients. CUCaNet is capable of adaptively learning
spectral and spatial response functions from HS-MS correspondences by enforcing
reasonable consistency assumptions on the networks. Moreover, a cross-attention
module is devised to yield more effective spatial-spectral information transfer
in networks. Extensive experiments are conducted on three widely-used HS-MS
datasets in comparison with state-of-the-art HSI-SR models, demonstrating the
superiority of the CUCaNet in the HSI-SR application. Furthermore, the codes
and datasets will be available at:
https://github.com/danfenghong/ECCV2020_CUCaNet
Bulk screening in core level photoemission from Mott-Hubbard and Charge-Transfer systems
We report bulk-sensitive hard X-ray ( = 5.95 KeV) core level
photoemission spectroscopy (PES) of single crystal VCrO
and the high- cuprate BiSrCaCuO (Bi2212).
VCrO exhibits low binding energy "satellites" to the V
"main lines" in the metallic phase, which are suppressed in the
antiferromagnetic insulator phase. In contrast, the Cu spectra of Bi2212
do not show temperature dependent features, but a comparison with soft X-ray
PES indicates a large increase in the "satellites" or weight
in the bulk. Cluster model calculations, including full multiplet structure and
a screening channel derived from the coherent band at the Fermi energy, give
very satisfactory agreement with experiments
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