23,337 research outputs found
Pseudogap and incommensurate magnetic fluctuations in YBa_2Cu_3O_{6. 6}
Unpolarized inelastic neutron scattering is used to study the temperature and
wave vector dependence of the dynamical magnetic susceptibility,
, of a well characterized single crystal
( K). We find that a pseudogap opens in the spin fluctuation spectrum
at temperatures well above . We speculate that the appearance of the low
frequency incommensurate fluctuations is associated with the opening of the
pseudogap. To within the error of the measurements, a gap in the spin
fluctuation spectrum is found in the superconducting state.Comment: 6 pages, 3 ps figs, Proceedings of ICNS, Physica B, to be publishe
Neutron Scattering Studies of the Magnetic Fluctuations in YBa_2Cu_3O_{7-\delta}
Neutron scattering measurements have been made on the spin fluctuations in
YBa_2Cu_3O_{7-\delta} for different oxygen doping levels. Incommensurability is
clearly observed for oxygen concentrations of 6.6 and 6.7 and is suggested for
the 6.93. Measurements of the resonance for the O_{6.6} concentration show that
it exists in a broadened and less intense form at temperatures much higher than
T_c.Comment: 9 pages, 4 gif figures, Proceedings of Spectroscopies in Novel
Superconductors, Cape Cod, Massachusetts, Sept, 199
Observation of Magnetic Moments in the Superconducting State of YBaCuO
Neutron Scattering measurements for YBaCuO have identified
small magnetic moments that increase in strength as the temperature is reduced
below and further increase below . An analysis of the data shows
the moments are antiferromagnetic between the Cu-O planes with a correlation
length of longer than 195 \AA in the - plane and about 35 \AA along the
c-axis. The origin of the moments is unknown, and their properties are
discusssed both in terms of Cu spin magnetism and orbital bond currents.Comment: 9 pages, and 4 figure
Near-Optimal Distributed Approximation of Minimum-Weight Connected Dominating Set
This paper presents a near-optimal distributed approximation algorithm for
the minimum-weight connected dominating set (MCDS) problem. The presented
algorithm finds an approximation in rounds,
where is the network diameter and is the number of nodes.
MCDS is a classical NP-hard problem and the achieved approximation factor
is known to be optimal up to a constant factor, unless P=NP.
Furthermore, the round complexity is known to be
optimal modulo logarithmic factors (for any approximation), following [Das
Sarma et al.---STOC'11].Comment: An extended abstract version of this result appears in the
proceedings of 41st International Colloquium on Automata, Languages, and
Programming (ICALP 2014
Semileptonic B decays into excited charmed mesons from QCD sum rules
Exclusive semileptonic decays into excited charmed mesons are studied
with QCD sum rules in the leading order of heavy quark effective theory. Two
universal Isgur-Wise functions \tau and \zeta for semileptonic B decays into
four lowest lying excited mesons (, , , and ) are
determined. The decay rates and branching ratios for these processes are
calculated.Comment: RevTeX, 17 pages including 2 figure
B decays to excited charm mesons
We review several aspects of the phenomenology of P-wave mesons:
mass splittings, effective strong couplings and leptonic constants. We also
describe a QCD sum rule determination to order of the form factor
governing the semileptonic decays to the charm doublet with
.Comment: LaTex, 3 pages, 1 figure. Talk given at 3rd International Conference
on Hyperons, Charm and Beauty Hadrons, Genoa, Italy, 30 Jun - 3 Jul 199
Magnetic Order in YBaCuO Superconductors
Polarized and unpolarized neutron diffraction has been used to search for
magnetic order in YBaCuO superconductors. Most of the
measurements were made on a high quality crystal of YBaCuO. It
is shown that this crystal has highly ordered ortho-II chain order, and a sharp
superconducting transition. Inelastic scattering measurements display a very
clean spin-gap and pseudogap with any intensity at 10 meV being 50 times
smaller than the resonance intensity. The crystal shows a complicated magnetic
order that appears to have three components. A magnetic phase is found at high
temperatures that seems to stem from an impurity with a moment that is in the
- plane, but disordered on the crystal lattice. A second ordering occurs
near the pseudogap temperature that has a shorter correlation length than the
high temperature phase and a moment direction that is at least partly along the
c-axis of the crystal. Its moment direction, temperature dependence, and Bragg
intensities suggest that it may stem from orbital ordering of the -density
wave (DDW) type. An additional intensity increase occurs below the
superconducting transition. The magnetic intensity in these phases does not
change noticeably in a 7 Tesla magnetic field aligned approximately along the
c-axis. Searches for magnetic order in YBaCuO show no signal
while a small magnetic intensity is found in YBaCuO that is
consistent with c-axis directed magnetic order. The results are contrasted with
other recent neutron measurements.Comment: 11 pages with 10 figure
DAMA/NaI results
The DAMA/NaI set-up of the DAMA experiment has been operative during seven
annual cycles and has investigated several rare processes. In particular, it
has been realised in order to investigate the model independent annual
modulation signature for Dark Matter particles in the galactic halo. With the
total exposure collected in the seven annual cycles (107731 kg day) a model
independent evidence for the presence of a Dark Matter particle component in
the galactic halo has been pointed out at 6.3 sigma C.L.. Some of the many
possible corollary model dependent quests for the candidate particle have been
presented as well.Comment: Contributed paper to the Rencontres de Moriond "Electroweak
Interactions and Unified Theories", La Thuile, Aosta Valley, Italy, March
200
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