8,310 research outputs found
A formula for charmonium suppression
In this work a formula for charmonium suppression obtained by Matsui in 1989
is analytically generalized for the case of complex c-cbar potential described
by a 3-dimensional and isotropic time-dependent harmonic oscillator (THO). It
is suggested that under certain conditions the formula can be applied to
describe J/\psi suppression in heavy-ion collisions at CERN-SPS, RHIC, and LHC
with the advantage of analytical tractability.Comment: 4 pages, no figures, to appear in Phys. At. Nucl., vol. 7
Real-Space Imaging of Alternate Localization and Extension of Quasi Two-Dimensional Electronic States at Graphite Surfaces in Magnetic Fields
We measured the local density of states (LDOS) of a quasi two-dimensional
(2D) electron system near point defects on a surface of highly oriented
pyrolytic graphite (HOPG) with scanning tunneling microscopy and spectroscopy.
Differential tunnel conductance images taken at very low temperatures and in
high magnetic fields show a clear contrast between localized and extended
spatial distributions of the LDOS at the valley and peak energies of the Landau
level spectrum, respectively. The localized electronic state has a single
circular distribution around the defects with a radius comparable to the
magnetic length. The localized LDOS is in good agreement with a spatial
distribution of a calculated wave function for a single electron in 2D in a
Coulomb potential in magnetic fields.Comment: 4 pages, 4 figure
Novel results in STM, ARPES, HREELS, Nernst, neutron, Raman, and isotope substitution experiments and their relation to bosonic modes and charge inhomogeneity, from perspective of negative-Ueff boson-fermion modelling of HTSC
This paper seeks to synthesize much recent work on the HTSC materials around
the latest STM results from Davis and coworkers. The conductance diffuse
scattering results in particular are used as point of entry to discuss bosonic
modes, both of condensed and uncondensed form. The bosonic mode picture is
essential to understanding an ever growing range of observations within the
HTSC field. The work is expounded within the context of the negative-U,
boson-fermion modelling long advocated by the author. This general approach is
presently seeing much theoretical development, into which I have looked to
couple many of the experimental advances. While the formal theory is not yet
sufficiently detailed to cover adequately all the experimental complexities
presented by the real cuprate systems, it is clear that it affords very
appreciable support to the line taken. An attempt is made throughout to say why
and how it is that these events are tied so very closely to this particular set
of materials.Comment: 36 pages pdf with 3 figures and 1 table included, Submitted to J.
Phys. Cond. Mat
Elastic Tensor of SrRuO
The six independent elastic constants of SrRuO were determined using
resonant ultrasound spectroscopy on a high-quality single-crystal specimen. The
constants are in excellent agreement with those obtained from pulse-echo
experiments performed on a sample cut from the same ingot. A calculation of the
Debye temperature using the measured constants agrees well with values obtained
from both specific heat and M\"{o}ssbauer measurements.Comment: 4 pages, 2 figures, 2 tables, submitted to PR
Angle-Resolved Photoemission Spectroscopy of the Antiferromagnetic Superconductor Nd1.87Ce0.13CuO4: Anisotropic Spin-Correlation Gap, Pseudogap, and the Induced Quasiparticle Mass Enhancement
We performed high-resolution angle-resolved photoemission spectroscopy on
Nd1.87Ce0.13CuO4, which is located at the boundary of the antiferromagnetic
(AF) and the superconducting phase. We observed that the quasiparticle (QP)
effective mass around (pi, 0) is strongly enhanced due to the opening of the AF
gap. The QP mass and the AF gap are found to be anisotropic, with the largest
value near the intersecting point of the Fermi surface and the AF zone
boundary. In addition, we observed that the QP peak disappears around the Neel
temperature (TN) while the AF pseudogap is gradually filled up at much higher
temperatures, possibly due to the short-range AF correlation.Comment: 4 pages, 4 figure
Doubly Perfect Nonlinear Boolean Permutations
Due to implementation constraints the XOR operation is widely used in order
to combine plaintext and key bit-strings in secret-key block ciphers. This
choice directly induces the classical version of the differential attack by the
use of XOR-kind differences. While very natural, there are many alternatives to
the XOR. Each of them inducing a new form for its corresponding differential
attack (using the appropriate notion of difference) and therefore block-ciphers
need to use S-boxes that are resistant against these nonstandard differential
cryptanalysis. In this contribution we study the functions that offer the best
resistance against a differential attack based on a finite field
multiplication. We also show that in some particular cases, there are robust
permutations which offers the best resistant against both multiplication and
exponentiation base differential attacks. We call them doubly perfect nonlinear
permutations
Transverse energy distributions and production in Pb+Pb collisions
We have analyzed the latest NA50 data on transverse energy distributions and
suppression in Pb+Pb collisions. The transverse energy distribution
was analysed in the geometric model of AA collisions. In the geometric model,
fluctuations in the number of NN collisions at fixed impact parameter are taken
into account. Analysis suggests that in Pb+Pb collisions, individual NN
collisions produces less , than in other AA collisions. The nucleons are
more transparent in Pb+Pb collisions. The transverse energy dependence of the
suppression was obtained following the model of Blaizot et al, where
charmonium suppression is assumed to be 100% effective above a threshold
density. With fluctuations in number of NN collisions taken into account, good
fit to the data is obtained, with a single parameter, the threshold density.Comment: Revised version with better E_T fit. 4 pages, 2 figure
BCS-like Bogoliubov Quasiparticles in High-Tc Superconductors Observed by Angle-Resolved Photoemission Spectroscopy
We performed high-resolution angle-resolved photoemission spectroscopy on
triple-layered high-Tc cuprate Bi2Sr2Ca2Cu3O10+delta. We have observed the full
energy dispersion (electron and hole branches) of Bogoliubov quasiparticles and
determined the coherence factors above and below EF as a function of momentum
from the spectral intensity as well as from the energy dispersion based on BCS
theory. The good quantitative agreement between the experiment and the
theoretical prediction suggests the basic validity of BCS formalism in
describing the superconducting state of cuprates.Comment: 4 pages, 3 figure
Description of hysteretic current-voltage characteristics of SNS junctions
Simplified model for current-voltage characteristics of weak links is
suggested. It is based on an approach considering the multiple Andreev
reflection in metallic Josephson junction. The model allows to calculate
current-voltage characteristics of the superconductor - normal metal -
superconductor junctions with different thicknesses of normal layer at
different temperatures. A hysteretic peculiarity of dependence is
described as result of the negative differential resistance. The
current-voltage characteristic of high- composite YBCO +BaPbO were
computed.Comment: 9 pages, 5 figures, submited to Supercond. Sci. Technol, replased
Fig.5 for more correct comparison with experimen
Bulk and surface low-energy excitations in YBa2Cu3O7-d studied by high-resolution angle-resolved photoemission spectroscopy
We have performed high-resolution angle-resolved photoemission spectroscopy
on YBa2Cu3O7-delta (Y123; delta = 0.06; Tc = 92 K). By accurately determining
the Fermi surface and energy band dispersion, we solve long-standing
controversial issues as to the anomalous electronic states of Y-based high-Tc
cuprates. We unambiguously identified surface-bilayer-derived bonding and
antibonding bands, together with their bulk counterparts. The surface bands are
highly overdoped (hole concentration x = 0.29), showing no evidence for the gap
opening or the dispersion anomaly in the antinodal region, while the bulk bands
show a clear dx2-y2-wave superconducting gap and the Bogoliubov
quasiparticle-like behavior with a characteristic energy scale of 50-60 meV
indicative of a strong electron-boson coupling in the superconducting state.
All these results suggest that the metallic and superconducting states coexist
at the adjacent bilayer of Y123 surface.Comment: Accepted for publication in Phys. Rev.
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