1,108 research outputs found
Theory of the beta-type Organic Superconductivity under Uniaxial Compression
We study theoretically the shift of the superconducting transition
temperature (Tc) under uniaxial compression in beta-type organic
superconductors, beta-(BEDT-TTF)2I3 and beta-(BDA-TTP)2X[X=SbF6,AsF6], in order
to clarify the electron correlation, the spin frustration and the effect of
dimerization. The transfer integrals are calculated by the extended Huckel
method assuming the uniaxial strain and the superconducting state mediated by
the spin fluctuation is solved using Eliashberg's equation with the
fluctuation-exchange approximation. The calculation is carried out on both the
dimerized (one-band) and nondimerized (two-band) Hubbard models. We have found
that (i) the behavior of Tc in beta-(BEDT-TTF)2I3 with a stronger dimerization
is well reproduced by the dimer model, while that in weakly dimerized
beta-BDA-TTP salts is rather well reproduced by the two-band model, and (ii)
the competition between the spin frustration and the effect induced by the
fluctuation is important in these materials, which causes nonmonotonic shift of
Tc against uniaxial compression.Comment: 18 pages, 16 figures, 2 tabl
Distorted wave impulse approximation analysis for spin observables in nucleon quasi-elastic scattering and enhancement of the spin-longitudinal response
We present a formalism of distorted wave impulse approximation (DWIA) for
analyzing spin observables in nucleon inelastic and charge exchange reactions
leading to the continuum. It utilizes response functions calculated by the
continuum random phase approximation (RPA), which include the effective mass,
the spreading widths and the \Delta degrees of freedom. The Fermi motion is
treated by the optimal factorization, and the non-locality of the
nucleon-nucleon t-matrix by an averaged reaction plane approximation. By using
the formalism we calculated the spin-longitudinal and the spin-transverse cross
sections, ID_q and ID_p, of 12C, 40Ca (\vec{p},\vec{n}) at 494 and 346 MeV. The
calculation reasonably reproduced the observed ID_q, which is consistent with
the predicted enhancement of the spin-longitudinal response function R_L.
However, the observed ID_p is much larger than the calculated one, which was
consistent with neither the predicted quenching nor the spin-transverse
response function R_T obtained by the (e,e') scattering. The Landau-Migdal
parameter g'_N\Delta for the N\Delta transition interaction and the effective
mass at the nuclear center m^*(r=0) are treated as adjustable parameters. The
present analysis indicates that the smaller g'_{N\Delta}(\approx 0.3) and
m^*(0) \approx 0.7 m are preferable. We also investigate the validity of the
plane wave impulse approximation (PWIA) with the effective nucleon number
approximation for the absorption, by means of which R_L and R_T have
conventionally been extracted.Comment: RevTex 3, 29 pages, 2 tables, 8 figure
Local Density Approximation for proton-neutron pairing correlations. I. Formalism
In the present study we generalize the self-consistent
Hartree-Fock-Bogoliubov (HFB) theory formulated in the coordinate space to the
case which incorporates an arbitrary mixing between protons and neutrons in the
particle-hole (p-h) and particle-particle (p-p or pairing) channels. We define
the HFB density matrices, discuss their spin-isospin structure, and construct
the most general energy density functional that is quadratic in local
densities. The consequences of the local gauge invariance are discussed and the
particular case of the Skyrme energy density functional is studied. By varying
the total energy with respect to the density matrices the self-consistent
one-body HFB Hamiltonian is obtained and the structure of the resulting mean
fields is shown. The consequences of the time-reversal symmetry, charge
invariance, and proton-neutron symmetry are summarized. The complete list of
expressions required to calculate total energy is presented.Comment: 22 RevTeX page
Comparison of 3-Dimensional and 1-Dimensional Schemes in the calculation of Atmospheric Neutrinos
A 3-dimensional calculation of atmospheric neutrinos flux is presented, and
the results are compared with those of a 1-dimensional one. In this study,
interaction and propagation of particles is treated in a 3-dimensional way
including the curvature of charged particles due to the geomagnetic field,
which is assumed to be a dipole field. The purpose of this paper is limited to
the comparison of calculation schemes. The updated flux value with new
interaction model and primary flux model will be reported in a separate paper.
Except for nearly horizontal directions, the flux is very similar to the
result of 1 dimensional calculations. However, for near-horizontal directions
an enhancement of the neutrino flux is seen even at energies as high as 1 GeV.
The production height of neutrinos is lower than the prediction by
1-dimensional calculation for near-horizontal directions, and is a little
higher for near-vertical directions. However, the difference is not evident
except for near-horizontal directions.Comment: 22 pages, 15figure
Superconductivity and a Mott Transition in a Hubbard Model on an Anisotropic Triangular Lattice
A half-filled-band Hubbard model on an anisotropic triangular lattice (t in
two bond directions and t' in the other) is studied using an optimization
variational Monte Carlo method, to consider the Mott transition and
superconductivity arising in \kappa-BEDT-TTF_2X. Adopting wave functions with
doublon-holon binding factors, we reveal that a first-order Mott
(conductor-to-nonmagnetic insulator) transition takes place at U=U_c
approximately of the band width, for a wide range of t'/t. This transition is
not directly connected to magnetism. Robust d-wave superconductivity appears in
a restricted parameter range: immediately below U_c and moderate strength of
frustration (0.4\lsim t'/t\lsim 0.7), where short-range antiferromagnetic
correlation sufficiently develops but does not come to a long-range order. The
relevance to experiments is also discussed.Comment: 15 pages, 17 figures, submitted to J. Phys. Soc. Jp
Measurement of the 8B Solar Neutrino Flux with the KamLAND Liquid Scintillator Detector
We report a measurement of the neutrino-electron elastic scattering rate from
8B solar neutrinos based on a 123 kton-day exposure of KamLAND. The
background-subtracted electron recoil rate, above a 5.5 MeV analysis threshold
is 1.49+/-0.14(stat)+/-0.17(syst) events per kton-day. Interpreted as due to a
pure electron flavor flux with a 8B neutrino spectrum, this corresponds to a
spectrum integrated flux of 2.77+/-0.26(stat)+/-0.32(syst) x 10^6 cm^-2s^-1.
The analysis threshold is driven by 208Tl present in the liquid scintillator,
and the main source of systematic uncertainty is due to background from
cosmogenic 11Be. The measured rate is consistent with existing measurements and
with Standard Solar Model predictions which include matter enhanced neutrino
oscillation.Comment: 6 pages, 3 figure
Quasi-Elastic Scattering in the Inclusive (He, t) Reaction
The triton energy spectra of the charge-exchange C(He,t) reaction
at 2 GeV beam energy are analyzed in the quasi-elastic nucleon knock-out
region. Considering that this region is mainly populated by the charge-exchange
of a proton in He with a neutron in the target nucleus and the final proton
going in the continuum, the cross-sections are written in the distorted-wave
impulse approximation. The t-matrix for the elementary exchange process is
constructed in the DWBA, using one pion- plus rho-exchange potential for the
spin-isospin nucleon- nucleon potential. This t-matrix reproduces the
experimental data on the elementary pn np process. The calculated
cross-sections for the C(He,t) reaction at to triton
emission angle are compared with the corresponding experimental data, and are
found in reasonable overall accord.Comment: 19 pages, latex, 11 postscript figures available at
[email protected], submitted to Phy.Rev.
A compact ultra-clean system for deploying radioactive sources inside the KamLAND detector
We describe a compact, ultra-clean device used to deploy radioactive sources
along the vertical axis of the KamLAND liquid-scintillator neutrino detector
for purposes of calibration. The device worked by paying out and reeling in
precise lengths of a hanging, small-gauge wire rope (cable); an assortment of
interchangeable radioactive sources could be attached to a weight at the end of
the cable. All components exposed to the radiopure liquid scintillator were
made of chemically compatible UHV-cleaned materials, primarily stainless steel,
in order to avoid contaminating or degrading the scintillator. To prevent radon
intrusion, the apparatus was enclosed in a hermetically sealed housing inside a
glove box, and both volumes were regularly flushed with purified nitrogen gas.
An infrared camera attached to the side of the housing permitted real-time
visual monitoring of the cable's motion, and the system was controlled via a
graphical user interface.Comment: Revised author affiliations, corrected typos, made minor improvements
to text, and revised reference
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