11,107 research outputs found
Filling dependence of a new type of charge ordered liquid on a triangular lattice system
We study the recently reported characteristic gapless charge ordered state in
a spinless fermion system on a triangular lattice under strong inter-site
Coulomb interactions. In this state the charges are spontaneously divided into
solid and liquid component, and the former solid part aligns in a Wigner
crystal manner while the latter moves among them like a pinball. We show that
such charge ordered liquid is stable over a wide range of filling, ,
and examine its filling dependent nature.Comment: 3 pages 3 figure
Spontaneous fourfold-symmetry breaking driven by electron-lattice coupling and strong correlations in high- cuprates
Using dynamical-mean-field theory for clusters, we study the two-dimensional
Hubbard model in which electrons are coupled with the orthorhombic lattice
distortions through the modulation in the hopping matrix. Instability towards
spontaneous symmetry breaking from a tetragonal symmetric phase to an
orthorhombic distorted phase is examined as a function of doping and
interaction strength. A very strong instability is found in the underdoped
pseudogap regime when the interaction strength is large enough to yield the
Mott insulating phase at half filling. The symmetry breaking accompanies the
recovery of quasiparticle weights along one of the two antinodal directions,
leading to the characteristic Fermi arc reconnection. We discuss the
implications of our results to the fourfold symmetry breaking reported in
systems where the underlying crystal does not have any structural anisotropy.Comment: 6 pages with 4 figure
Comment on ``Spin Dependent Hopping and Colossal Negative Magnetoresistance in Epitaxial Films in Fields up to 50 T''
Recently Wagner et al. [Phys. Rev. Lett. Vol. 81, P. 3980 (1998)] proposed
that Mott's original model be modified to incorporate a hopping barrier which
depends on the misorientation between the spins of electrons at the initial and
the final states in an elementary process. They further claimed that using the
model they can explain the observed scaling behavior--
negative-magnetoresistivity scaling proportional to the Brillouin function
in the ferromagnetic state and to in the paramagnetic
state. In this comment we argue that the modification needed for Mott's
original model is different from that proposed by Wagner et al. and further
show that our picture will successfully explain the observed scaling in the two
regimes.Comment: 1 pag
Theory of electromagnon in the multiferroic Mn perovskites: Vital role of higher harmonic components of the spiral spin order
We study theoretically the electromagnon and its optical spectrum (OS) of the
terahertz-frequency regime in the magnetic-spiral-induced multiferroic phases
of the rare-earth (R) Mn perovskites, RMnO3, taking into account the elliptical
deformation or the higher harmonics of the spiral spin configuration, which has
been missed so far. A realistic spin Hamiltonian, which gives phase diagrams in
agreement with experiments, resolves a long standing puzzle, i.e., the
double-peak structure of the OS with a larger low-energy peak originating from
magnon modes hybridized with the zone-edge state. We also predict the magnon
branches associated with the electromagnon, which can be tested by
neutron-scattering experiment.Comment: 5 pages, 4 figure
Photo-induced insulator-metal transition of a spin-electron coupled system
The photo-induced metal-insulator transition is studied by the numerical
simulation of real-time quantum dynamics of a double-exchange model. The
spatial and temporal evolutions of the system during the transition have been
revealed including (i) the threshold behavior with respect to the intensity and
energy of light, (ii) multiplication of particle-hole (p-h) pairs by a p-h pair
of high energy, and (iii) the space-time pattern formation such as (a) the
stripe controlled by the polarization of light, (b) coexistence of metallic and
insulating domains, and (c) dynamical spontaneous symmetry-breaking associated
with the spin spiral formation imposed by the conservation of total spin for
small energy-dissipation rates
Critical Exponents of the Metal-Insulator Transition in the Two-Dimensional Hubbard Model
We study the filling-controlled metal-insulator transition in the
two-dimensional Hubbard model near half-filling with the use of zero
temperature quantum Monte Carlo methods. In the metallic phase, the
compressibility behaves as where
is the critical chemical potential. In the insulating phase, the
localization length follows with . Under the assumption of hyperscaling, the compressibility
data leads to a correlation length exponent . Our
results show that the exponents and agree within
statistical uncertainty. This confirms the assumption of hyperscaling with
correlation length exponent and dynamical exponent . In
contrast the metal-insulator transition in the generic band insulators in all
dimensions as well as in the one-dimensional Hubbard model satisfy the
hyperscaling assumption with exponents and .Comment: Two references added. The DVI file and PS figure files are also
available at http://www.issp.u-tokyo.ac.jp/labs/riron/imada/furukawa/; to
appear in J. Phys. Soc. Jpn 65 (1996) No.
Universality Class of Ferromagnetic Transition in Three-Dimensional Double-Exchange System - O(N) Monte Carlo Study -
Curie temperature and exponents are studied for the three-dimensional
double-exchange model. Applying the O(N) Monte Carlo algorithm, we perform
systematic finite-size scaling analyses on the data up to sites. The
obtained values of the critical exponents are consistent with those of the
Heisenberg universality class, and clearly distinct from the mean-field values.Comment: 3 pages including 2 figure
- …