1,672 research outputs found
Defect and anisotropic gap induced quasi-one-dimensional modulation of local density of states in YBaCuO
Motivated by recent angle-resolved photoemission spectroscopy (ARPES)
measurement that superconducting YBaCuO (YBCO) exhibits a
-symmetry gap, we show possible quasi-one-dimensional
modulations of local density of states in YBCO. These aniostropic gap and
defect induced stripe structures are most conspicuous at higher biases and
arise due to the nesting effect associated with a Fermi liquid. Observation of
these spectra by scanning tunneling microscopy (STM) would unify the picture
among STM, ARPES, and inelastic neutron scattering for YBCO.Comment: 4 pages, 4 figure
Chasing the identification of ASCA Galactic Objects (ChIcAGO): An X-ray survey of unidentified sources in the galactic plane. I : Source sample and initial results
We present the Chasing the Identification of ASCA Galactic Objects (ChIcAGO) survey, which is designed to identify the unknown X-ray sources discovered during the ASCA Galactic Plane Survey (AGPS). Little is known about most of the AGPS sources, especially those that emit primarily in hard X-rays (2-10 keV) within the Fx 10-13 to 10-11 erg cm -2 s-1 X-ray flux range. In ChIcAGO, the subarcsecond localization capabilities of Chandra have been combined with a detailed multiwavelength follow-up program, with the ultimate goal of classifying the >100 unidentified sources in the AGPS. Overall to date, 93 unidentified AGPS sources have been observed with Chandra as part of the ChIcAGO survey. A total of 253 X-ray point sources have been detected in these Chandra observations within 3′ of the original ASCA positions. We have identified infrared and optical counterparts to the majority of these sources, using both new observations and catalogs from existing Galactic plane surveys. X-ray and infrared population statistics for the X-ray point sources detected in the Chandra observations reveal that the primary populations of Galactic plane X-ray sources that emit in the Fx 10-13 to 10-11 erg cm -2 s-1 flux range are active stellar coronae, massive stars with strong stellar winds that are possibly in colliding wind binaries, X-ray binaries, and magnetars. There is also another primary population that is still unidentified but, on the basis of its X-ray and infrared properties, likely comprises partly Galactic sources and partly active galactic nuclei.Peer reviewedSubmitted Versio
Oxygen defect in YBa\u3csub\u3e2\u3c/sub\u3eCu\u3csub\u3e3\u3c/sub\u3eO\u3csub\u3ex\u3c/sub\u3e: An x-ray photoemission approach
A combined x-ray photoemission and diamagnetic-susceptibility study of YBa2Cu3Ox with x≃6 and 7 has been performed, with emphasis on the oxygen defect and the effect of heating in vacuum. By comparing spectra taken at these two oxygen contents, the core levels observed in the O 1s and Ba 4d spectral range are identified. Peak-intensity analysis indicates (1) that the oxygen released during the in situ heating is derived from or near the Cu-O-Cu-O chains of YBa2Cu3O7 and (2) that there is a random distribution of oxygen defects in or near these chains leading to two chemically dissimilar barium atoms even in single-orthorhombic-phase samples
The Electric Dipole Moment of the Nucleons in Holographic QCD
We introduce the strong CP-violation in the framework of AdS/QCD model and
calculate the electric dipole moments of nucleons as well as the CP-violating
pion-nucleon coupling. Our holographic estimate of the electric dipole moments
gives for the neutron d_n=1.08 X 10^{-16} theta (e cm), which is comparable
with previous estimates. We also predict that the electric dipole moment of the
proton should be precisely the minus of the neutron electric dipole moment,
thus leading to a new sum rule on the electric dipole moments of baryons.Comment: 22 pages, no figures. v2: A reference and an acknowledgment added.
v3: One more reference, to appear in JHE
Spin-current induced electric field
We theoretically predict that a pure steady state spin-current without
charge-current can induce an electric field. A formula for the induced electric
field is derived and we investigate its characteristics. Conversely, a moving
spin is affected by an external electric field and we present a formula for the
interaction energy.Comment: 4 pages, 2 figure
Hole Superconductivity in : a high cuprate without Cu
The theory of hole superconductivity explains high temperature
superconductivity in cuprates as driven by pairing of hole carriers in oxygen
orbitals in the highly negatively charged planes. The pairing
mechanism is hole undressing and is Coulomb-interaction driven. We propose that
the planes of atoms in are akin to the planes without ,
and that the recently observed high temperature superconductivity in
arises similarly from undressing of hole carriers in the planar boron
orbitals in the negatively charged planes. Doping with electrons
and with holes should mirror the behavior of underdoped and overdoped high
cuprates respectively. We discuss possible ways to achieve higher
transition temperatures in boron compounds based on this theory.Comment: A section on isotope effect has been added, as well as other minor
change
Inflationary Attractor in Braneworld Scenario
We demonstrate the attractor behavior of inflation driven by a scalar field
or a tachyon field in the context of recently proposed four-dimensional
effective gravity induced on the world-volume of a three-brane in
five-dimensional Einstein gravity, and we obtain a set of exact inflationary
solutions. Phase portraits indicate that an initial kinetic term decays rapidly
and it does not prevent the onset of inflation. The trajectories more rapidly
reach the slow-roll curve than in the standard cosmology.Comment: 7 pages, 8 figures, RevTeX, to appear in Phys. Rev. D69 (2004
Effect of Dynamical SU(2) Gluons to the Gap Equation of Nambu--Jona-Lasinio Model in Constant Background Magnetic Field
In order to estimate the effect of dynamical gluons to chiral condensate, the
gap equation of SU(2) gauged Nambu--Jona-Lasinio model, under a constant
background magnetic field, is investigated up to the two-loop order in 2+1 and
3+1 dimensions. We set up a general formulation allowing both cases of electric
as well as magnetic background field. We rely on the proper time method to
maintain gauge invariance. In 3+1 dimensions chiral symmetry breaking
(SB) is enhanced by gluons even in zero background magnetic field and
becomes much striking as the background field grows larger. In 2+1 dimensions
gluons also enhance SB but whose dependence on the background field is
not simple: dynamical mass is not a monotone function of background field for a
fixed four-fermi coupling.Comment: 20 pages, 5 figure
Segregation by thermal diffusion of an intruder in a moderately dense granular fluid
A solution of the inelastic Enskog equation that goes beyond the weak
dissipation limit and applies for moderate densities is used to determine the
thermal diffusion factor of an intruder immersed in a dense granular gas under
gravity. This factor provides a segregation criterion that shows the transition
between the Brazil-nut effect (BNE) and the reverse Brazil-nut effect (RBNE) by
varying the parameters of the system (masses, sizes, density and coefficients
of restitution). The form of the phase-diagrams for the BNE/RBNE transition
depends sensitively on the value of gravity relative to the thermal gradient,
so that it is possible to switch between both states for given values of the
parameters of the system. Two specific limits are considered with detail: (i)
absence of gravity, and (ii) homogeneous temperature. In the latter case, after
some approximations, our results are consistent with previous theoretical
results derived from the Enskog equation. Our results also indicate that the
influence of dissipation on thermal diffusion is more important in the absence
of gravity than in the opposite limit. The present analysis extends previous
theoretical results derived in the dilute limit case [V. Garz\'o, Europhys.
Lett. {\bf 75}, 521 (2006)] and is consistent with the findings of some recent
experimental results.Comment: 10 figure
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