1,288 research outputs found
Quantum Noise Limits for Nonlinear, Phase-Invariant Amplifiers
Any quantum device that amplifies coherent states of a field while preserving
their phase generates noise. A nonlinear, phase-invariant amplifier may
generate less noise, over a range of input field strengths, than any linear
amplifier with the same amplification. We present explicit examples of such
nonlinear amplifiers, and derive lower bounds on the noise generated by a
nonlinear, phase-invariant quantum amplifier.Comment: RevTeX, 6 pages + 4 figures (included in file; hard copy sent on
request
Half-Periodic Josephson Effect in an s-Wave Superconductor - Normal Metal -d-Wave Superconductor Junction
We predict that the Josephson current in a clean s-wave superconductor-normal
metal-d-wave superconductor junction is periodic in superconducting phase
difference with period instead of . The frequency of
non-stationary Josephson effect is correspondingly The
effect is due to coexistence in the normal layer of current carrying Andreev
levels with phase differences and Comment: 4 pages, REVTeX, 3 figure
Synthesis, structure and electrochemical behaviour of Na, Mg-II, Mn-II, Cd-II and Ni-II complexes of 3-(2-carboxyphenylhydrazone)pentane-2,4-dione
Mononuclear manganese(II) [Mn(kappa O-HL)(2)(CH3OH)(4)] (4), nickel(II) [Ni(kappa O-2, kappa N-L)(H2O)(3)] (5), cadmium(II) [Cd(kappa O-2-HL)(2)(CH3OH)(3)] (7), tetranuclear zinc(II) [Zn-4(mu-OH)(2)(1 kappa O:2 kappa O-HL)(4)(kappa O-HL)(2)(H2O)(4)] (6) and polynuclear aqua sodium(I) [Na(H2O)(2)(mu-H2O)(2)](n)(HL)(n) (2) and magnesium(II) [Mg(OH)(H2O)(mu-H2O)(2)](n)(-HL)(n) (3) complexes were synthesized using 3-(2-carboxyphenyl-hydrazone)pentane-2,4-dione (H2L, 1) as a ligand precursor. The complexes were characterized by single crystal X-ray diffraction, elemental analysis, IR, H-1 and C-13 NMR (for 2, 3, 6 and 7) spectroscopies. Mono- or dianionic deprotonated derivatives of H2L display different coordination modes and lead to topologies and nuclearities of the complexes depending on metal ions and conditions used for the syntheses. Extensive intermolecular H-bonds form supramolecular arrangements in 1D chains (4 and 6), 1D chains of the organic anion and 2D networks of the metal-aqua aggregates (2 and 3), 2D networks (7) or even 3D frameworks (5). Electrochemical studies, by cyclic voltammetry and controlled potential electrolysis, show ligand centred redox processes as corroborated by theoretical DFT calculations in terms of LUMO and HOMO compositions. (C) 2012 Elsevier Ltd. All rights reserved
Interlayer pair tunneling and gap anisotropy in YBaCuO
Recent ARPES measurement observed a large -axis gap anisotropy,
, in clean YBaCuO. This
indicates that some sub-dominant component may exist in the -wave
dominant gap. We propose that the interlayer pairing tunneling contribution can
be determined through the investigation of the order parameter anisotropy.
Their potentially observable features in transport and spin dynamics are also
studied.Comment: 4 pages, 3 figure
Asymmetric magnetic interference patterns in 0-pi Josephson junctions
We examine the magnetic interference patterns of Josephson junctions with a
region of 0- and of pi-phase shift. Such junctions have recently been realized
as c-axis YBCO-Pb junctions with a single twin boundary in YBCO. We show that
in general the junction generates self-fields which introduces an asymmetry in
the critical current under reversal of the magnetic field. Numerical
calculations of these asymmetries indicate they account well for the
unexplained features observed in single twin boundary junctions.Comment: 4 pages, 3 figure
Upturn observed in heavy nuclei to iron ratios by the ATIC-2 experiment
The ratios of fluxes of heavy nuclei from sulfur (Z=16) to chromium (Z=24) to
the flux of iron were measured by the ATIC-2 experiment. The ratios are
decreasing functions of energy from 5 GeV/n to approximately 80 GeV/n, as
expected. However, an unexpected sharp upturn in the ratios are observed for
energies above 100 GeV/n for all elements from Z=16 to Z=24. Similar upturn but
with lower amplitude was also discovered in the ATIC-2 data for the ratio of
fluxes of abundant even nuclei (C, O, Ne, Mg, Si) to the flux of iron.
Therefore the spectrum of iron is significantly different from the spectra of
other abundant even nuclei.Comment: 4 pages, LaTeX2e, a paper for 23rd European Cosmic Ray Symposium
(2012
Lowering the Light Speed Isotropy Limit: European Synchrotron Radiation Facility Measurements
The measurement of the Compton edge of the scattered electrons in GRAAL
facility in European Synchrotron Radiation Facility (ESRF) in Grenoble with
respect to the Cosmic Microwave Background dipole reveals up to 10 sigma
variations larger than the statistical errors. We now show that the variations
are not due to the frequency variations of the accelerator. The nature of
Compton edge variations remains unclear, thus outlining the imperative of
dedicated studies of light speed anisotropy
Possible structure in the cosmic ray electron spectrum measured by the ATIC-2 and ATIC-4 experiments
A strong excess in a form of a wide peak in the energy range of 300-800 GeV
was discovered in the first measurements of the electron spectrum in the energy
range from 20 GeV to 3 TeV by the balloon-borne experiment ATIC (J. Chang et
al. Nature, 2008). The experimental data processing and analysis of the
electron spectrum with different criteria for selection of electrons,
completely independent of the results reported in (J. Chang et al. Nature,
2008) is employed in the present paper. The new independent analysis generally
confirms the results of (J. Chang et al. Nature, 2008), but shows that the
spectrum in the region of the excess is represented by a number of narrow
peaks. The measured spectrum is compared to the spectrum of (J. Chang et al.
Nature, 2008) and to the spectrum of the Fermi/LAT experiment.Comment: LaTeX2e, 10 pages, 4 figures, a paper for ECRS 2010 (Turku, Finland);
http://www.astrophys-space-sci-trans.net/7/119/2011
Effect of anisotropy on universal transport in unconventional superconductors
We investigate the universal electronic transport for a mixed
+s-wave superconductor in the presence of an anisotropic
elliptical Fermi surface. Similar to the universal low-temperature transport
predicted in a -wave superconductor with a circular Fermi surface,
anisotropic universal features are found in the low-temperature microwave
conductivity, and thermal conductivity in the anisotropic system. The effects
of anisotropy on the penetration depth, impurity induced suppression, and
the zero-frequency density of states are also considered. While a small amount
of anisotropy can lead to a strong suppression of the effective scattering rate
and hence the density of states at zero frequency, experimental data suggests
that large effects are restored by a negative -component gap admixture.Comment: 8 page
Fermi Surface and gap parameter in high-Tc superconductors: the Stripe Quantum Critical Point scenario
We study the single-particle spectral properties of electrons coupled to
quasicritical charge and spin fluctuations close to a stripe-phase, which is
governed by a Quantum Critical Point near optimum doping. We find that spectral
weight is transferred from the quasiparticle peak to incoherent dispersive
features. As a consequence the distribution of low-laying spectral weight is
modified with respect to the quasiparticle Fermi surface. The interplay of
charge and spin fluctuations reproduces features of the observed Fermi surface,
such as the asymmetric suppression of spectral weight near the M points of the
Brillouin zone.
Within the model, we also analyze the interplay between repulsive spin and
attractive charge fluctuations in determining the symmetry and the peculiar
momentum dependence of the superconducting gap parameter. When both spin and
charge fluctuations are coupled to the electrons, we find -wave
gap symmetry in a wide range of parameter. A crossover - vs -wave
symmetry of the gap may occur when the strength of charge fluctuations
increases with respect to spin fluctuations.Comment: 18 pages, 3 included figures, to be published on Physica
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