3,475 research outputs found
Parameters for Systems Exhibiting Local Lattice Distortions, Charge and Spin Ordering
Keeping in mind the experimental results that indicate local lattice
distortions, charge and spin orderings, we have developed a phenomenological
approach which allows us to describe the electronic phase diagram of cuprates
and related systems in terms of few parameters.In the present work we consider
a third-order parameter theory which characterize charge, spin and
superconductivity orderings. We are thus led to a theory of three scalar
fields. By coupling these scalars to gauge fields we are naturally led to
string-like solutions, which we interpret as stripes. This ties nicely with our
quantum group conjecture that 1d systems play an important role in the physics
of cuprates and related materials. We show that this simple approach can give
rough values for two-order parameters which can be naively be interpreted as
charge and spin orderings. We also report our attempt to understand how local
lattice distortions are involved and what role they play in terms of these two
order parameters.Comment: 8 pages revtex, Published in AIP Conference Proceedings 554: Int.
Sym. on Physics in Local Lattice Distortions, July 23-26, 200
Stripe formation in high-Tc superconductors
The non-uniform ground state of the two-dimensional three-band Hubbard model
for the oxide high-Tc superconductors is investigated using a variational Monte
Carlo method. We examine the effect produced by holes doped into the
antiferromagnetic (AF) background in the underdoped region. It is shown that
the AF state with spin modulations and stripes is stabilized du to holes
travelling in the CuO plane. The structures of the modulated AF spins are
dependent upon the parameters used in the model. The effect of the boundary
conditions is reduced for larger systems. We show that there is a region where
incommensurability is proportional to the hole density. Our results give a
consistent description of stripes observed by the neutron- scattering
experiments based on the three-band model for CuO plane.Comment: 8 pages, 9 figure
Locally Optimal Control of Quantum Systems with Strong Feedback
For quantum systems with high purity, we find all observables that, when
continuously monitored, maximize the instantaneous reduction in the von Neumann
entropy. This allows us to obtain all locally optimal feedback protocols with
strong feedback, and explicit expressions for the best such protocols for
systems of size N <= 4. We also show that for a qutrit the locally optimal
protocol is the optimal protocol for a given range of control times, and derive
an upper bound on all optimal protocols with strong feedback.Comment: 4 pages, Revtex4. v2: published version (some errors corrected
Off-diagonal Wave Function Monte Carlo Studies of Hubbard Model I
We propose a Monte Carlo method, which is a hybrid method of the quantum
Monte Carlo method and variational Monte Carlo theory, to study the Hubbard
model. The theory is based on the off-diagonal and the Gutzwiller type
correlation factors which are taken into account by a Monte Carlo algorithm. In
the 4x4 system our method is able to reproduce the exact results obtained by
the diagonalization. An application is given to investigate the half-filled
band case of two-dimensional square lattice. The energy is favorably compared
with quantum Monte Carlo data.Comment: 9 pages, 11 figure
PMD1 THE NEW METHOD FOR TIME ADJUSTMENT OF THE NUMBER NEEDED TO TREAT AND ITS APPLICATION TO PHARMACOECONOMICS ANALYSIS
Effects of energy dependence in the quasiparticle density of states on far-infrared absorption in the pseudogap state
We derive a relationship between the optical conductivity scattering rate
1/\tau(\omega) and the electron-boson spectral function \alpha^2F(\Omega) valid
for the case when the electronic density of states, N(\epsilon), cannot be
taken as constant in the vicinity of the Fermi level. This relationship turned
out to be useful for analyzing the experimental data in the pseudogap state of
cuprate superconductors.Comment: 8 pages, RevTeX4, 1 EPS figure; final version published in PR
Fermi arc in doped high-Tc cuprates
We propose a -density wave induced by the spin-orbit coupling in the CuO
plane. The spectral function of high-temperature superconductors in the under
doped and lightly doped regions is calculated in order to explain the Fermi arc
spectra observed recently by angle-resolved photoemission spectroscopy. We take
into account the tilting of CuO octahedra as well as the on-site
Coulombrepulsive interaction; the tilted octahedra induce the staggered
transfer integral between orbitals and Cu orbitals, and
bring about nontrivial effects of spin-orbit coupling for the electrons in
the CuO plane. The spectral weight shows a peak at around (,) for
light doping and extends around this point forming an arc as the carrier
density increases, where the spectra for light doping grow continuously to be
the spectra in the optimally doped region. This behavior significantly agrees
with that of the angle-resolved photoemissionspectroscopy spectra. Furthermore,
the spin-orbit term and staggered transfer effectively induce a flux state, a
pseudo-gap with time-reversal symmetry breaking. We have a nodal metallic state
in the light-doping case since the pseudogap has a symmetry.Comment: 5 pages, 7 figure
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