12,365 research outputs found
Momentum-resolved charge excitations in high-Tc cuprates studied by resonant inelastic x-ray scattering
We report a Cu K-edge resonant inelastic x-ray scattering (RIXS) study of
high-Tc cuprates. Momentum-resolved charge excitations in the CuO2 plane are
examined from parent Mott insulators to carrier-doped superconductors. The Mott
gap excitation in undoped insulators is found to commonly show a larger
dispersion along the [pi,pi] direction than the [pi,0] direction. On the other
hand, the resonance condition displays material dependence. Upon hole doping,
the dispersion of the Mott gap excitation becomes weaker and an intraband
excitation appears as a continuum intensity below the gap at the same time. In
the case of electron doping, the Mott gap excitation is prominent at the zone
center and a dispersive intraband excitation is observed at finite momentum
transfer
Observation of Conduction Band Satellite of Ni Metal by 3p-3d Resonant Inverse Photoemission Study
Resonant inverse photoemission spectra of Ni metal have been obtained across
the Ni 3 absorption edge. The intensity of Ni 3 band just above Fermi
edge shows asymmetric Fano-like resonance. Satellite structures are found at
about 2.5 and 4.2 eV above Fermi edge, which show resonant enhancement at the
absorption edge. The satellite structures are due to a many-body configuration
interaction and confirms the existence of 3 configuration in the ground
state of Ni metal.Comment: 4 pages, 3 figures, submitted to Physical Review Letter
Static quark free energies at finite temperature with two flavors of improved Wilson quarks
Polyakov loop correlations at finite temperature in two-flavor QCD are
studied in lattice simulations with the RG-improved gluon action and the
clover-improved Wilson quark action. From the simulations on a
lattice, we extract the free energies, the effective running coupling and the Debye screening mass for various color channels of
heavy quark--quark and quark--anti-quark pairs above the critical temperature.
The free energies are well approximated by the screened Coulomb form with the
appropriate Casimir factors. The magnitude and the temperature dependence of
the Debye mass are compared to those of the next-to-leading order thermal
perturbation theory and to a phenomenological formula given in terms of . Also we made a comparison between our results with the Wilson quark
and those with the staggered quark previously reported.Comment: 7 pages, 9 figures, talk given at Lattice 2006 (high temperature and
density
Finite temperature phase transition of two-flavor QCD with an improved Wilson quark action
We study the phase structure of QCD at finite temperatures with two flavors
of dynamical quarks on a lattice with the size , using a renormalization group improved gauge action and a clover improved
Wilson quark action. The simulations are made along the lines of constant
physics determined in terms of at zero-temperature. We
show preliminary results for the spatial string tension in the high temperature
phase.Comment: 7 pages, 7 figures, talk presented at Lattice 2006 (high temperature
and density
Thermodynamics and heavy-quark free energies at finite temperature and density with two flavors of improved Wilson quarks
Thermodynamics of two-flavor QCD at finite temperature and density is studied
on a lattice, using a renormalization group improved gauge
action and the clover improved Wilson quark action. In the simulations along
lines of constant , we calculate the Taylor expansion
coefficients of the heavy-quark free energy with respect to the quark chemical
potential () up to the second order. By comparing the expansion
coefficients of the free energies between quark()and antiquark(),
and between and , we find a characteristic difference at finite
due to the first order coefficient of the Taylor expansion. We also calculate
the quark number and isospin susceptibilities, and find that the second order
coefficient of the quark number susceptibility shows enhancement around the
pseudo-critical temperature.Comment: Talk given at the XXV International Symposium on Lattice Field Theory
(Lattice 2007), July 30 - August 4, 2007, Regensburg, German
Mott gap excitations in twin-free YBa2Cu3O7-d (Tc = 93 K) studied by RIXS
Mott gap excitations in the high-Tc superconductor of the optimal doped
YBa2Cu3O7-d (Tc = 93 K) have been studied by the resonant inelastic x-ray
scattering method. Anisotropic spectra in the ab-plane are observed in a
twin-free crystal. The excitation from the one-dimensional CuO chain is
enhanced at 2 eV near the zone boundary of the b* direction, while the
excitation from the CuO2 plane is broad at 1.5-4 eV and almost independent of
the momentum transfer. Theoretical calculation based on the one-dimensional and
two-dimensional Hubbard model reproduces the observed spectra by taking the
different parameters of the on-site Coulomb energy. The fact of the Mott gap of
the CuO chain site is much smaller than that of CuO2 plane site is observed for
the first time
Nuclear Force from Monte Carlo Simulations of Lattice Quantum Chromodynamics
The nuclear force acting between protons and neutrons is studied in the Monte
Carlo simulations of the fundamental theory of the strong interaction, the
quantum chromodynamics defined on the hypercubic space-time lattice. After a
brief summary of the empirical nucleon-nucleon (NN) potentials which can fit
the NN scattering experiments in high precision, we outline the basic
formulation to derive the potential between the extended objects such as the
nucleons composed of quarks. The equal-time Bethe-Salpeter amplitude is a key
ingredient for defining the NN potential on the lattice. We show the results of
the numerical simulations on a lattice with the lattice spacing fm (lattice volume (4.4 fm)) in the quenched approximation.
The calculation was carried out using the massively parallel computer Blue
Gene/L at KEK. We found that the calculated NN potential at low energy has
basic features expected from the empirical NN potentials; attraction at long
and medium distances and the repulsive core at short distance. Various future
directions along this line of research are also summarized.Comment: 13 pages, 4 figures, version accepted for publication in
"Computational Science & Discovery" (IOP
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