45 research outputs found
Analysis of the vertexes , and radiative decays ,
In this article, we study the vertexes and with the light-cone QCD sum rules, then assume the vector meson
dominance of the intermediate , and , and
calculate the radiative decays and .Comment: 28 pages, 4 tables, revised versio
Magnetotransport in a bi-crystal film of La_0.7Sr_0.3MnO_3
Transport properties of an epitaxial film of La_0.7Sr_0.3MnO_3 (LSMO),
deposited epitaxially on a LaAlO_3 bi-crystal substrate having a misorientation
angle of 9.2 deg., have been studied.
The film was patterned into a meander containing 100 grain boundaries. The
resistivity of the sample exhibits two components; one originating from the
grain boundary regions, and one from the LSMO elements in the meander; the
latter contribution is similar to the resistivity of a reference epitaxial LSMO
film. The low (<0.5 T) and high (up to 6 T) field magnetoresistance was also
studied. The meander show a large low field magnetoresistance, increasing with
decreasing temperature, and a constant high field slope of the
magnetoconductance, results that are well explained by a two-step spin
polarized tunneling model.Comment: ICM2000 contribution - 6 pages, 3 figure
Depairing critical currents and self-magnetic field effects in submicron YBa₂Cu₃O₇₋δ microbridges and bicrystal junctions
We report on depairing critical currents in submicron YBa₂Cu₃O₇₋δ microbridges. A small-angle
bicrystal grain boundary junction is used as a tool to study the entrance of vortices induced by
a transport current and their influence on the I–V curves. The interplay between the depairing and
the vortex motion determines a crossover in the temperature dependence of the critical current.
The high entrance field of vortices in very narrow superconducting channels creates the possibility
of carrying a critical current close to the depairing limit determined by the S–S–S nature of the
small-angle grain boundary junction
Theory of c-axis Josephson tunneling in d-wave superconductors
The temperature and angular dependence of the c-axis Josephson current and
the superfluid density in layered d-wave superconductors are studied within the
framework of an extended Ambegaokar-Baratoff formalism. In particular, the
effects of angle-dependent tunneling matrix elements and Andreev scattering at
grain boundaries are taken into account. These lead to strong corrections of
the low-temperature behavior of the plasma frequency and the Josephson current.
Recent c-axis measurements on the cuprate high-temperature superconductors
HgBa_2CaCu_{1+\delta} and Bi_2Sr_2CaCu_2O_{8+\delta} can therefore be
interpreted to be consistent with a d-wave order parameter.Comment: Revtex, 4 pages with 4 eps figures, to appear in PRB R
Tilt Grain-Boundary Effects in S- and D-Wave Superconductors
We calculate the s- and d-wave superconductor order parameter in the vicinity
of a tilt grain boundary. We do this self-consistently within the Bogoliubov de
Gennes equations, using a realistic microscopic model of the grain boundary. We
present the first self-consistent calculations of supercurrent flows in such
boundaries, obtaining the current-phase characteristics of grain boundaries in
both s-wave and d-wave superconductors
Rare Decays of \Lambda_b->\Lambda + \gamma and \Lambda_b ->\Lambda + l^{+} l^{-} in the Light-cone Sum Rules
Within the Standard Model, we investigate the weak decays of and with the light-cone
sum rules approach. The higher twist distribution amplitudes of
baryon to the leading conformal spin are included in the sum rules for
transition form factors. Our results indicate that the higher twist
distribution amplitudes almost have no influences on the transition form
factors retaining the heavy quark spin symmetry, while such corrections can
result in significant impacts on the form factors breaking the heavy quark spin
symmetry. Two phenomenological models (COZ and FZOZ) for the wave function of
baryon are also employed in the sum rules for a comparison, which can
give rise to the form factors approximately 5 times larger than that in terms
of conformal expansion. Utilizing the form factors calculated in LCSR, we then
perform a careful study on the decay rate, polarization asymmetry and
forward-backward asymmetry, with respect to the decays of , .Comment: 38 pages, 15 figures, some typos are corrected and more references
are adde
Heavy quarkonium: progress, puzzles, and opportunities
A golden age for heavy quarkonium physics dawned a decade ago, initiated by
the confluence of exciting advances in quantum chromodynamics (QCD) and an
explosion of related experimental activity. The early years of this period were
chronicled in the Quarkonium Working Group (QWG) CERN Yellow Report (YR) in
2004, which presented a comprehensive review of the status of the field at that
time and provided specific recommendations for further progress. However, the
broad spectrum of subsequent breakthroughs, surprises, and continuing puzzles
could only be partially anticipated. Since the release of the YR, the BESII
program concluded only to give birth to BESIII; the -factories and CLEO-c
flourished; quarkonium production and polarization measurements at HERA and the
Tevatron matured; and heavy-ion collisions at RHIC have opened a window on the
deconfinement regime. All these experiments leave legacies of quality,
precision, and unsolved mysteries for quarkonium physics, and therefore beg for
continuing investigations. The plethora of newly-found quarkonium-like states
unleashed a flood of theoretical investigations into new forms of matter such
as quark-gluon hybrids, mesonic molecules, and tetraquarks. Measurements of the
spectroscopy, decays, production, and in-medium behavior of c\bar{c}, b\bar{b},
and b\bar{c} bound states have been shown to validate some theoretical
approaches to QCD and highlight lack of quantitative success for others. The
intriguing details of quarkonium suppression in heavy-ion collisions that have
emerged from RHIC have elevated the importance of separating hot- and
cold-nuclear-matter effects in quark-gluon plasma studies. This review
systematically addresses all these matters and concludes by prioritizing
directions for ongoing and future efforts.Comment: 182 pages, 112 figures. Editors: N. Brambilla, S. Eidelman, B. K.
Heltsley, R. Vogt. Section Coordinators: G. T. Bodwin, E. Eichten, A. D.
Frawley, A. B. Meyer, R. E. Mitchell, V. Papadimitriou, P. Petreczky, A. A.
Petrov, P. Robbe, A. Vair
Nonlinear dielectric response of c- and a-axis oriented epitaxial (Ba,Sr)TiO3 layers between metallic oxide electrodes
Trilayer epitaxial heterostructures of SrRuO3/(700nm)BaxSr1-xTiO3/SrRuOx3 (x= 0.25 ; 0.8) have been grown by laser ablation on (001)LSATO. Both ferroelectric and oxide metallic layers in the trilayer heterostructure possess granular structure. The grains (100-200 nm) in the ferroelectric layer were well in-plane and out-of-plane oriented and separated by low angle grain boundaries. Orientation of the polar axis in the ferroelectric layer was dependent on the type of mechanical stresses (tensile or compressive). When in paraelectric state, BaxSrl-xTiO3 layers followed a Curie - Weiss behavior with Weiss temperature and Curie constant roughly matching those of a bulk single crystal. The dielectric constant of the c-axis oriented Ba0.25Sr0.75TiO, layers was tuned in the range 3700ε0 - 450ε0 if +/- 2.5V if a bias voltage between +2.5V and -2.5V was applied to the electrodes. The loss factor, tan δ for the ferroelectric layers peaked at temperatures below the phase transition point. The peak falls at lower temperature at lower frequency and is affected by a bias voltage