8,943 research outputs found
Magnetism and Superconductivity in a Two-band Hubbard Model in Infinite Dimensions
We study a two-band Hubbard model using the dynamical mean-field theory
combined with the exact diagonalization method. At the electron density ,
a transition from a band-insulator to a correlated semimetal occurs when the
on-site Coulomb interaction is varied for a fixed value of the
charge-transfer energy . At low temperature, the correlated semimetal
shows ferromagnetism or superconductivity. With increasing doping , the
ferromagnetic transition temperature rapidly decreases and finally becomes zero
at a critical value of . The second-order phase transition occurs at high
temperature, while a phase separation of ferromagnetic and paramagnetic states
takes place at low temperature. The superconducting transition temperature
gradually decreases and finally becomes zero near () where the
system is Mott insulator which shows antiferromagnetism at low temperature.Comment: 3 pages, 5 figures, proceedings of the International Conference on
Strongly Correlated Electrons with Orbital Degrees of Freedom (ORBITAL2001
Charge Gap in the One-Dimensional Extended Hubbard Model at Quarter Filling
We propose a new combined approach of the exact diagonalization, the
renormalization group and the Bethe ansatz for precise estimates of the charge
gap in the one-dimensional extended Hubbard model with the onsite and
the nearest-neighbor interactions and at quarter filling. This approach
enables us to obtain the absolute value of including the prefactor
without ambiguity even in the critical regime of the metal-insulator transition
(MIT) where is exponentially small, beyond usual renormalization group
methods and/or finite size scaling approaches. The detailed results of
down to of order of near the MIT are shown as contour lines on the
- plane.Comment: 4 pages, 4 figure
Random matrix model at nonzero chemical potentials with anomaly effects
Phase diagram of the chiral random matrix model with U(1)A breaking term is
studied with the quark chemical potentials varied independently at zero
temperature, by taking the chiral and meson condensates as the order
parameters. Although, without the U(1)A breaking term, chiral transition of
each flavor can happen separately responding to its chemical potential, the
U(1)A breaking terms mix the chiral condensates and correlate the phase
transitions. In the three flavor case, we find that there are mixings between
the meson and chiral condensates due to the U(1)A anomaly, which makes the
meson condensed phase more stable. Increasing the hypercharge chemical
potential () with the isospin and quark chemical potentials (,
) kept small, we observe that the kaon condensed phase becomes the
ground state and at the larger the pion condense phase appears
unexpectedly, which is caused by the competition between the chiral restoration
and the meson condensation. The similar happens when and are
exchanged, and the kaon condensed phase becomes the ground state at larger
below the full chiral restoration.Comment: 12 pages, 8 figure
Combined Analysis of Numerical Diagonalization and Renormalization Group methods for the One-Dimensional - Model at Quarter filling
The one-dimensional extended Hubbard model with both the on-site and the
nearest neighbor interactions at quarter filling is studied by using a
novel finite size scaling. We diagonalize finite size systems numerically and
calculate the Luttinger-liquid parameter which is substituted into
the renormalization group equation as an initial condition. It leads
in the infinite size system and the result agrees very well with the available
exact result with . This approach also yields the charge gap in the
insulating state near the metal-insulator transition where the characteristic
energy becomes exponentially small and the usual finite size scaling is not
applicable.Comment: 7 pages, 8 figures,submitted to PR
Recombining Plasma & Gamma-ray Emission in the Mixed-morphology Supernova Remnant 3C 400.2
3C 400.2 belongs to the mixed morphology supernova remnant class, showing
center-filled X-ray and shell-like radio morphology. We present a study of 3C
400.2 with archival Suzaku and Fermi-LAT observations. We find recombining
plasma (RP) in the Suzaku spectra of north-east and south-east regions. The
spectra of these regions are well described by two-component thermal plasma
models: The hard component is in RP, while the soft component is in collisional
ionization equilibrium (CIE) conditions. The RP has enhanced abundances
indicating that the X-ray emission has an ejecta origin, while the CIE has
solar abundances associated with the interstellar material. The X-ray spectra
of north-west and south-west regions are best fitted by a two-component thermal
plasma model: an ionizing and a CIE plasma. We have detected GeV gamma-ray
emission from 3C 400.2 at the level of 5 assuming a point-like
source model with a power-law (PL) type spectrum. We have also detected a new
GeV source at the level of 13 assuming a Gaussian extension model
with a PL type spectrum in the neighborhood of the SNR. We report the analysis
results of 3C 400.2 and the new extended gamma-ray source and discuss the
nature of gamma-ray emission of 3C 400.2 in the context of existing NANTEN CO
data, DRAO HI data, and the Suzaku X-ray analysis results.Comment: Accepted to be published in the Astrophysical Journa
Dynamics of a deformable self-propelled domain
We investigate the dynamical coupling between the motion and the deformation
of a single self-propelled domain based on two different model systems in two
dimensions. One is represented by the set of ordinary differential equations
for the center of gravity and two tensor variables characterizing deformations.
The other is an active cell model which has an internal mechanism of motility
and is represented by the partial differential equation for deformations.
Numerical simulations show a rich variety of dynamics, some of which are common
to the two model systems. The origin of the similarity and the difference is
discussed.Comment: 6 pages, 6 figure
- …