185 research outputs found
Simulation Studies on the Stability of the Vortex-Glass Order
The stability of the three-dimensional vortex-glass order in random type-II
superconductors with point disorder is investigated by equilibrium Monte Carlo
simulations based on a lattice XY model with a uniform field threading the
system. It is found that the vortex-glass order, which stably exists in the
absence of screening, is destroyed by the screenng effect, corroborating the
previous finding based on the spatially isotropic gauge-glass model. Estimated
critical exponents, however, deviate considerably from the values reported for
the gauge-glass model.Comment: Minor modifications made, a few referenced added; to appear in J.
Phys. Soc. Jpn. Vol.69 No.1 (2000
Effects of point defects on the phase diagram of vortex states in high-Tc superconductors in B//c axis
The phase diagram for the vortex states of high- superconductors
with point defects in axis is drawn by large-scale Monte
Carlo simulations. The vortex slush (VS) phase is found between the vortex
glass (VG) and vortex liquid (VL) phases. The first-order transition between
this novel normal phase and the VL phase is characterized by a sharp jump of
the density of dislocations. The first-order transition between the Bragg glass
(BG) and VG or VS phases is also clarified. These two transitions are compared
with the melting transition between the BG and VL phases.Comment: 4 pages, 9 eps figures (included in text), uses revtex.sty, overall
changes with several additional data points, though conclusion is unchange
Vortex State and Field-Angle Resolved Specific Heat Oscillation for H // ab in d-Wave Superconductors
When magnetic field is applied parallel to the ab plane in d_{x^2-y^2}-wave
superconductors, the transition of stable vortex lattice structure, spatial
structure of local density of states, and specific heat oscillation by rotation
of magnetic field orientation are investigated by quantitative calculations
based on the selfconsistent Eilenberger theory. We estimate how the vortex
state changes depending on the relative angle between the node-direction of the
superconducting gap and magnetic field orientation. To reproduce the
sign-change of specific heat oscillation observed in CeCoIn_5, our study is
done by including strong paramagnetic effect. The quantitative theoretical
calculations give decisive information to analyze the experimental data on the
field-angle dependence, and establish the angle-resolved specific heat
experiment as a spectroscopic means to identify the node-position of the
superconducting gap.Comment: 9 pages, 13 figure
Sub-millimeter Observations of Giant Molecular Clouds in the Large Magellanic Cloud: Temperature and Density as Determined from J=3-2 and J=1-0 transitions of CO
We have carried out sub-mm 12CO(J=3-2) observations of 6 giant molecular
clouds (GMCs) in the Large Magellanic Cloud (LMC) with the ASTE 10m sub-mm
telescope at a spatial resolution of 5 pc and very high sensitivity. We have
identified 32 molecular clumps in the GMCs and revealed significant details of
the warm and dense molecular gas with n(H2) 10 cm and
Tkin 60 K. These data are combined with 12CO(J=1-0) and 13CO(J=1-0)
results and compared with LVG calculations. We found that the ratio of
12CO(J=3-2) to 12CO(J=1-0) emission is sensitive to and is well correlated with
the local Halpha flux. We interpret that differences of clump propeties
represent an evolutionary sequence of GMCs in terms of density increase leading
to star formation.Type I and II GMCs (starless GMCs and GMCs with HII regions
only, respectively) are at the young phase of star formation where density does
not yet become high enough to show active star formation and Type III GMCs
(GMCs with HII regions and young star clusters) represents the later phase
where the average density is increased and the GMCs are forming massive stars.
The high kinetic temperature correlated with \Halpha flux suggests that FUV
heating is dominant in the molecular gas of the LMC.Comment: 74 pages, including 41 figures, accepted for publication in ApJ
Vortex Line Fluctuations in Model High Temperature Superconductors
We carry out Monte Carlo simulations of the uniformly frustrated 3d XY model
as a model for vortex line fluctuations in a high Tc superconductor. A density
of vortex lines of f=1/25 is considered. We find two sharp phase transitions.
The low T phase is an ordered vortex line lattice. The high T normal phase is a
vortex line liquid with much entangling, cutting, and loop excitations. An
intermediate phase is found which is characterized as a vortex line liquid of
disentangled lines. In this phase, the system displays superconducting
properties in the direction parallel to the magnetic field, but normal behavior
in planes perpendicular to the magnetic field.Comment: 38 pages, LaTeX 15 figures (upon request to
[email protected]
Measurement of Inclusive Production of Neutral Pions from Upsilon(4S) Decays
Using the Belle detector operating at the KEKB e+e- storage ring, we have
measured the mean multiplicity and the momentum spectrum of neutral pions from
the decays of the Upsilon(4S) resonance. We measure a mean of 4.70 +/- 0.04 +/-
0.22 neutral pions per Upsilon(4S) decay.Comment: 15 pages, 4 figs. Submitted to Phys.Rev.
Observation of Large CP Violation in the Neutral B Meson System
We present a measurement of the Standard Model CP violation parameter sin
2phi_1 based on a 29.1 fb^{-1} data sample collected at the Upsilon(4S)
resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider.
One neutral B meson is fully reconstructed as a J/psi Ks, psi(2S) Ks, chi_c1
Ks, eta_c Ks, J/psi K_L or J/psi K^{*0} decay and the flavor of the
accompanying B meson is identified from its decay products. From the asymmetry
in the distribution of the time intervals between the two B meson decay points,
we determine sin 2phi_1 = 0.99 +- 0.14(stat) +- 0.06(syst). We conclude that we
have observed CP violation in the neutral B meson system.Comment: 4 figures, to appear in Phys. Rev. Letter
A Measurement of the Branching Fraction for the Inclusive B --> X(s) gamma Decays with the Belle Detector
We have measured the branching fraction of the inclusive radiative B meson
decay B --> X(s) gamma to be Br(B->X(s)gamma)=(3.36 +/- 0.53(stat) +/-
0.42(sys) +0.50-0.54(th)) x 10^{-4}.
The result is based on a sample of 6.07 x 10^6 BBbar events collected at the
Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric e^+e^-
storage ring.Comment: 14 pages, 6 Postsript figures, uses elsart.cl
Measurement of B0d - B0d-bar mixing rate from the time evolution of dilepton events at the Upsilon(4S)
We report a determination of the B0d - B0d-bar mixing parameter Delta-m_d
based on the time evolution of dilepton yields in Upsilon(4S) decays. The
measurement is based on a 5.9 /fb data sample collected by the Belle detector
at KEKB. The proper-time difference distributions for same-sign and
opposite-sign dilepton events are simultaneously fitted to an expression
containing Delta-m_d as a free parameter. Using both muons and electrons, we
obtain Delta-m_d = 0.463 +- 0.008(stat.) +- 0.016(sys.) ps^{-1} This is the
first determination of Delta-m_d from time evolution measurements at the
Upsilon(4S). We also place limits on possible CPT violations.Comment: 12 pages, 2 figure
Measurement of the CP Violation Parameter sin(2phi_1) in B^0_d Meson Decays
We present a measurement of the Standard Model CP violation parameter
sin(2phi_1) based on a 10.5 fb^{-1} data sample collected at the Upsilon(4S)
resonance with the Belle detector at the KEKB asymmetric e+e- collider. One
neutral B meson is reconstructed in the J/psi K_S, psi(2S) K_S, chi_{c1} K_S,
eta_c K_S, J/psi K_L or J/psi pi^0 CP-eigenstate decay channel and the flavor
of the accompanying B meson is identified from its charged particle decay
products. From the asymmetry in the distribution of the time interval between
the two B-meson decay points, we determine sin(2phi_1) = 0.58 +0.32-0.34 (stat)
+0.09-0.10 (syst).Comment: LaTex, 13 pages, 3 figures, submitted to P.R.
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