2,499 research outputs found
Demonstration of a robust pseudogap in a three-dimensional correlated electronic system
We outline a partial-fractions decomposition method for determining the
one-particle spectral function and single-particle density of states of a
correlated electronic system on a finite lattice in the non self-consistent
T-matrix approximation to arbitrary numerical accuracy, and demonstrate the
application of these ideas to the attractive Hubbard model. We then demonstrate
the effectiveness of a finite-size scaling ansatz which allows for the
extraction of quantities of interest in the thermodynamic limit from this
method. In this approximation, in one or two dimensions, for any finite lattice
or in the thermodynamic limit, a pseudogap is present and its energy diverges
as Tc is approached from above; this is an unphysical manifestation of using an
approximation that predicts a spurious phase transition in one or two
dimensions. However, in three dimensions one expects the transition predicted
by this approximation to represent a true continuous phase transition, and in
the thermodynamic limit any pseudogap predicted by this formulation will remain
finite. We have applied our method to the attractive Hubbard model on a
three-dimensional simple cubic lattice, and find that for intermediate coupling
a prominent pseudogap is found in the single-particle density of states, and
this gap persists over a large temperature range. In addition, we also show
that for weak coupling a pseudogap is also present. The pseudogap energy at the
transition temperature is almost a factor of three larger than the T=0 BCS gap
for intermediate coupling, whereas for weak coupling the pseudogap and BCS gap
energies are essentially equal.Comment: 28 pages, 9 figure
Spin dynamics in the antiferromagnetic phase for electron-doped cuprate superconductors
Based on the --- model we have calculated the dynamical spin
susceptibilities in the antiferromagnetic (AF) phase for electron-doped
cuprates, by use of the slave-boson mean-field theory and random phase
approximation. Various results for the susceptibilities versus energy and
momentum have been shown at different dopings. At low energy, except the
collective spin-wave mode around and 0, we have primarily observed
that new resonance peaks will appear around and equivalent
points with increasing doping, which are due to the particle-hole excitations
between the two AF bands. The peaks are pronounced in the transverse
susceptibility but not in the longitudinal one. These features are predicted
for neutron scattering measurements.Comment: 5 pages, 3 figures, published version with minor change
Achieving growth within the UK's Domestic Energy Efficiency Retrofitting Services sector, practitioner experiences and strategies moving forward
Direct-laser writing for subnanometer focusing and single-molecule imaging
Two-photon direct laser writing is an additive fabrication process that utilizes two-photon absorption of tightly focused femtosecond laser pulses to implement spatially controlled polymerization of a liquid-phase photoresist. Two-photon direct laser writing is capable of nanofabricating arbitrary three-dimensional structures with nanometer accuracy. Here, we explore direct laser writing for high-resolution optical microscopy by fabricating unique 3D optical fiducials for single-molecule tracking and 3D single-molecule localization microscopy. By having control over the position and three-dimensional architecture of the fiducials, we improve axial discrimination and demonstrate isotropic subnanometer 3D focusing (<0.8 nm) over tens of micrometers using a standard inverted microscope. We perform 3D single-molecule acquisitions over cellular volumes, unsupervised data acquisition and live-cell single-particle tracking with nanometer accuracy
Dynamical properties of the single--hole -- model on a 32--site square lattice
We present results of an exact diagonalization calculation of the spectral
function for a single hole described by the -- model
propagating on a 32--site square cluster. The minimum energy state is found at
a crystal momentum , consistent with
theory, and our measured dispersion relation agrees well with that determined
using the self--consistent Born approximation. In contrast to smaller cluster
studies, our spectra show no evidence of string resonances. We also make a
qualitative comparison of the variation of the spectral weight in various
regions of the first Brillouin zone with recent ARPES data.Comment: 10 pages, 5 postscript figures include
Magnetic susceptibility of a CuO2 plane in the La2CuO4 system: I. RPA treatment of the Dzyaloshinskii-Moriya Interactions
Motivated by recent experiments on undoped La2CuO4, which found pronounced
temperature-dependent anisotropies in the low-field magnetic susceptibility, we
have investigated a two-dimensional square lattice of S=1/2 spins that interact
via Heisenberg exchange plus the symmetric and anti-symmetric
Dzyaloshinskii-Moriya anisotropies. We describe the transition to a state with
long-ranged order, and find the spin-wave excitations, with a mean-field
theory, linear spin-wave analysis, and using Tyablikov's RPA decoupling scheme.
We find the different components of the susceptibility within all of these
approximations, both below and above the N'eel temperature, and obtain evidence
of strong quantum fluctuations and spin-wave interactions in a broad
temperature region near the transition.Comment: 20 pages, 2 column format, 22 figure
Tsetse Genetics: Contributions to Biology, Systematics, and Control of Tsetse Flies
Tsetse flies (Diptera: Glossinidae) constitute a small, ancient taxon of exclusively hematophagous insects that reproduce slowly and viviparously. Because tsetse flies are the only vectors of pathogenic African trypanosomes, they are a potent and constant threat to humans and livestock over much of sub-Saharan Africa. Despite their low fecundity, tsetse flies demonstrate great resilience, which makes population suppression expensive, transient, and beyond the capacities of private and public sectors to accomplish, except over small areas. Nevertheless, control measures that include genetic methods are under consideration at national and supranational levels. There is a pressing need for sufficient laboratory cultures of tsetse flies and financial support to carry out genetic research. Here we review tsetse genetics from organismal and population points of view and identify some research needs
Ultrafast generation of highly crystalline graphene quantum dots from graphite paper via laser writing
Graphene quantum dots (GQDs) are attractive fluorescent nanoparticles that have wide applicability, are inexpensive, nontoxic, photostable, water-dispersible, biocompatible and environmental-friendly. Various strategies for the synthesis of GQDs have been reported. However, simple and efficient methods of producing GQDs with control over the size of the GQDs, and hence their optical properties, are sorely needed. Herein, an ultra-fast and efficient laser writing technique is presented as a means to produce GQDs with homogeneous size from graphene produced by the instantaneous photothermal gasification and recrystallization mechanism. Controlling the laser scan speed and output power, the yield of GQDs can reach to be about 31.458 mg/s, which shows promising potential for large-scale production. The entire process eliminates the need for chemical solvents or any other reagents. Notably, the prepared laser writing produced GQDs (LWP-GQDs) exhibit blue fluorescence under UV irradiation of 365 nm and the Commission Internationale de L'Eclairage (CIE) chromaticity coordinates is measured at (0.1721, 0.123). Overall, this method exhibits superior advantages over the complex procedures and low yields required by other existing methods, and thus has great potential for the commercial applications
Comparative judgments are more consistent than binary classification for labelling word complexity
© 2019 Association for Computational Linguistics Lexical simplification systems replace complex words with simple ones based on a model of which words are complex in context. We explore how users can help train complex word identification models through labelling more efficiently and reliably. We show that using an interface where annotators make comparative rather than binary judgments leads to more reliable and consistent labels, and explore whether comparative judgments may provide a faster way for collecting labels
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