32 research outputs found
Large Orbital Magnetic Moment and Coulomb Correlation effects in FeBr2
We have performed an all-electron fully relativistic density functional
calculation to study the magnetic properties of FeBr2. We show for the first
time that the correlation effect enhances the contribution from orbital degrees
of freedom of electrons to the total magnetic moment on Fe as
opposed to common notion of nearly total quenching of the orbital moment on
Fe site. The insulating nature of the system is correctly predicted when
the Hubbard parameter U is included. Energy bands around the gap are very
narrow in width and originate from the localized Fe-3 orbitals, which
indicates that FeBr2 is a typical example of the Mott insulator.Comment: 4 pages, 3 figures, revtex4, PRB accepte
Histogram Monte Carlo study of multicritical behavior in the hexagonal easy-axis Heisenberg antiferromagnet
The results of a detailed histogram Monte-Carlo study of critical-fluctuation
effects on the magnetic-field temperature phase diagram associated with the
hexagonal Heisenberg antiferromagnet with weak axial anisotropy are reported.
The multiphase point where three lines of continuous transitions merge at the
spin-flop boundary exhibits a structure consistent with scaling theory but
without the usual umbilicus as found in the case of a bicritical point.Comment: 7 pages (RevTex 3.0), 1 figure available upon request, CRPS-93-1
Dynamic scaling and aging phenomena in short-range Ising spin glass: CuCoCl-FeCl graphite bi-intercalation compound
Static and dynamic behavior of short-range Ising-spin glass
CuCoCl-FeCl graphite bi-intercalation compounds
(GBIC) has been studied with SQUID DC and AC magnetic susceptibility. The
dependence of the zero-field relaxation time above a spin-freezing
temperature (= 3.92 0.11 K) is well described by critical slowing
down. The absorption below decreases with
increasing angular frequency , which is in contrast to the case of 3D
Ising spin glass. The dynamic freezing temperature at which
dd, is determined as a function of
frequency (0.01 Hz 1 kHz) and magnetic field (0 5 kOe). The dynamic scaling analysis of the relaxation time
defined as at suggests the absence of
SG phase in the presence of (at least above 100 Oe). Dynamic scaling
analysis of and near
leads to the critical exponents ( = 0.36 0.03, = 3.5
0.4, = 1.4 0.2, = 6.6 1.2, = 0.24
0.02, and = 0.13 0.02). The aging phenomenon is studied through
the absorption below . It obeys a
power-law decay with an exponent . The rejuvenation effect is also observed under
sufficiently large (temperature and magnetic-field) perturbations.Comment: 14 pages, 19 figures; to be published in Phys. Rev. B (September 1,
2003
First Observation of Coherent Production in Neutrino Nucleus Interactions with 2 GeV
The MiniBooNE experiment at Fermilab has amassed the largest sample to date
of s produced in neutral current (NC) neutrino-nucleus interactions at
low energy. This paper reports a measurement of the momentum distribution of
s produced in mineral oil (CH) and the first observation of coherent
production below 2 GeV. In the forward direction, the yield of events
observed above the expectation for resonant production is attributed primarily
to coherent production off carbon, but may also include a small contribution
from diffractive production on hydrogen. Integrated over the MiniBooNE neutrino
flux, the sum of the NC coherent and diffractive modes is found to be (19.5
1.1 (stat) 2.5 (sys))% of all exclusive NC production at
MiniBooNE. These measurements are of immediate utility because they quantify an
important background to MiniBooNE's search for
oscillations.Comment: Submitted to Phys. Lett.
Quantum walks: a comprehensive review
Quantum walks, the quantum mechanical counterpart of classical random walks,
is an advanced tool for building quantum algorithms that has been recently
shown to constitute a universal model of quantum computation. Quantum walks is
now a solid field of research of quantum computation full of exciting open
problems for physicists, computer scientists, mathematicians and engineers.
In this paper we review theoretical advances on the foundations of both
discrete- and continuous-time quantum walks, together with the role that
randomness plays in quantum walks, the connections between the mathematical
models of coined discrete quantum walks and continuous quantum walks, the
quantumness of quantum walks, a summary of papers published on discrete quantum
walks and entanglement as well as a succinct review of experimental proposals
and realizations of discrete-time quantum walks. Furthermore, we have reviewed
several algorithms based on both discrete- and continuous-time quantum walks as
well as a most important result: the computational universality of both
continuous- and discrete- time quantum walks.Comment: Paper accepted for publication in Quantum Information Processing
Journa
Measurement of and charged current inclusive cross sections and their ratio with the T2K off-axis near detector
We report a measurement of cross section and the first measurements of the cross section
and their ratio
at (anti-)neutrino energies below 1.5
GeV. We determine the single momentum bin cross section measurements, averaged
over the T2K -flux, for the detector target material (mainly
Carbon, Oxygen, Hydrogen and Copper) with phase space restricted laboratory
frame kinematics of 500 MeV/c. The
results are and $\sigma(\nu)=\left( 2.41\
\pm0.022{\rm{(stat.)}}\pm0.231{\rm (syst.)}\ \right)\times10^{-39}^{2}R\left(\frac{\sigma(\bar{\nu})}{\sigma(\nu)}\right)=
0.373\pm0.012{\rm (stat.)}\pm0.015{\rm (syst.)}$.Comment: 18 pages, 8 figure
Test of Lorentz and CPT violation with Short Baseline Neutrino Oscillation Excesses
The sidereal time dependence of MiniBooNE electron neutrino and anti-electron
neutrino appearance data are analyzed to search for evidence of Lorentz and CPT
violation. An unbinned Kolmogorov-Smirnov test shows both the electron neutrino
and anti-electron neutrino appearance data are compatible with the null
sidereal variation hypothesis to more than 5%. Using an unbinned likelihood fit
with a Lorentz-violating oscillation model derived from the Standard Model
Extension (SME) to describe any excess events over background, we find that the
electron neutrino appearance data prefer a sidereal time-independent solution,
and the anti-electron neutrino appearance data slightly prefer a sidereal
time-dependent solution. Limits of order 10E-20 GeV are placed on combinations
of SME coefficients. These limits give the best limits on certain SME
coefficients for muon neutrino to electron neutrino and anti-muon neutrino to
anti-electron neutrino oscillations. The fit values and limits of combinations
of SME coefficients are provided.Comment: 14 pages, 3 figures, and 2 tables, submitted to Physics Letters
Search for astrophysical electron antineutrinos in Super-Kamiokande with 0.01wt% gadolinium-loaded water
We report the first search result for the flux of astrophysical electron
antineutrinos for energies O(10) MeV in the gadolinium-loaded Super-Kamiokande
(SK) detector. In June 2020, gadolinium was introduced to the ultra-pure water
of the SK detector in order to detect neutrons more efficiently. In this new
experimental phase, SK-Gd, we can search for electron antineutrinos via inverse
beta decay with efficient background rejection and higher signal efficiency
thanks to the high efficiency of the neutron tagging technique. In this paper,
we report the result for the initial stage of SK-Gd with a exposure at 0.01% Gd mass concentration. No significant excess
over the expected background in the observed events is found for the neutrino
energies below 31.3 MeV. Thus, the flux upper limits are placed at the 90%
confidence level. The limits and sensitivities are already comparable with the
previous SK result with pure-water () owing
to the enhanced neutron tagging
Search for Lorentz and CPT violation using sidereal time dependence of neutrino flavor transitions over a short baseline
A class of extensions of the Standard Model allows Lorentz and CPT violations, which can be identified
by the observation of sidereal modulations in the neutrino interaction rate. A search for such modulations
was performed using the T2K on-axis near detector. Two complementary methods were used in this study,
both of which resulted in no evidence of a signal. Limits on associated Lorentz and CPT-violating terms
from the Standard Model extension have been derived by taking into account their correlations in this
model for the first time. These results imply such symmetry violations are suppressed by a factor of more
than 10 20 at the GeV scale