1,034 research outputs found
Effects of Next-Nearest-Neighbor Repulsion on One-Dimensional Quarter-Filled Electron Systems
We examine effects of the next-nearest-neighbor repulsion on electronic
states of a one-dimensional interacting electron system which consists of
quarter-filled band and interactions of on-site and nearest-neighbor repulsion.
We derive the effective Hamiltonian for the electrons around wave number \pm
\kf (\kf: Fermi wave number) and apply the renormalization group method to
the bosonized Hamiltonian. It is shown that the next-nearest-neighbor repulsion
makes 4\kf-charge ordering unstable and suppresses the spin fluctuation.
Further the excitation gaps and spin susceptibility are also evaluated.Comment: 19 pages, 8 figures, submitted to J. Phys. Soc. Jp
Computer simulations on sprite initiation for realistic lightning models with higher‐frequency surges
[1] Computer simulations on transient luminous emissions in the mesosphere and lower ionosphere have been performed for realistic lightning modelings with fast-varying current surges (M components) superimposed on the lightning continuing current (CC). The algorithm used here is an electromagnetic (EM) code, which enables us to estimate self-consistently the reduced electric field, electron density, conductivity, and luminosity as a function of space and time by solving the Maxwell equations. It is found that M components in the CC with small amplitudes, but with a fast-varying EM effect, can initiate or enhance the occurrence of sprites. Even for a return stroke (RS) without CC, subsequent high-frequency current variations (like M components) are found to lead to dramatic changes in the sprite occurrence. The physics underlying these changes is studied by means of, e.g., temporal and spatial variations of luminosity, electron density, and conductivity. As the conclusion, the RS is a fundamental agency for spites, but high-frequency variations as EM effects exhibit an additional essential influence on sprite occurrence. These computational results are used to offer some useful ideas concerning the unsolved problems of sprites and halos, including polarity asymmetry, long-delay characteristics, and morphological shapes of sprites
Correlation Effects in a One-Dimensional Quarter-Filled Electron System with Repulsive Interactions
A one-dimensional electron system at quarter-filling has been examined by
applying the renormalization group method to a bosonized model with on-site (U)
and nearest-neighbor (V) repulsive interactions. By evaluating both normal
scattering and Umklapp scattering perturbatively, we obtain a phase diagram in
which a metallic state with a 2k_F spin density wave (k_F is the Fermi wave
number) moves into an insulating state with charge disproportionation of a 4k_F
charge density wave with an increase in both U and V. The effect of the
next-nearest-neighbor repulsion is also discussed.Comment: 4 pages, 2 figures, to be published in J. Phys. Soc. Jpn. 69 (2000)
No.
Finite-temperature phase transitions in quasi-one-dimensional molecular conductors
Phase transitions in 1/4-filled quasi-one-dimensional molecular conductors
are studied theoretically on the basis of extended Hubbard chains including
electron-lattice interactions coupled by interchain Coulomb repulsion. We apply
the numerical quantum transfer-matrix method to an effective one-dimensional
model, treating the interchain term within mean-field approximation.
Finite-temperature properties are investigated for the charge ordering, the
"dimer Mott" transition (bond dimerization), and the spin-Peierls transition
(bond tetramerization). A coexistent state of charge order and bond
dimerization exhibiting dielectricity is predicted in a certain parameter
range, even when intrinsic dimerization is absent.Comment: to be published in J. Phys. Soc. Jpn., Vol. 76 (2007) No. 1 (5 pages,
4 figures); typo correcte
Tricritical Behavior in Charge-Order System
Tricritical point in charge-order systems and its criticality are studied for
a microscopic model by using the mean-field approximation and exchange Monte
Carlo method in the classical limit as well as by using the Hartree-Fock
approximation for the quantum model. We study the extended Hubbard model and
show that the tricritical point emerges as an endpoint of the first-order
transition line between the disordered phase and the charge-ordered phase at
finite temperatures. Strong divergences of several fluctuations at zero
wavenumber are found and analyzed around the tricritical point. Especially, the
charge susceptibility chi_c and the susceptibility of the next-nearest-neighbor
correlation chi_R are shown to diverge and their critical exponents are derived
to be the same as the criticality of the susceptibility of the double occupancy
chi_D0. The singularity of conductivity at the tricritical point is clarified.
We show that the singularity of the conductivity sigma is governed by that of
the carrier density and is given as
|sigma-sigma_c|=|g-g_c|^{p_t}Alog{|g-g_{c}|}+B), where g is the effective
interaction of the Hubbard model, sigma_c g_c represents the critical
conductivity(interaction) and A and B are constants, respectively. Here, in the
canonical ensemble, we obtain p_t=2beta_t=1/2 at the tricritical point. We also
show that p_t changes into p_{t}'=2beta=1 at the tricritical point in the
grand-canonical ensemble when the tricritical point in the canonical ensemble
is involved within the phase separation region. The results are compared with
available experimental results of organic conductor (DI-DCNQI)2Ag.Comment: 20 pages, 32 figures, to appear in J. Phys. Soc. Jpn.
Vol.75(2006)No.
Effect of nearest neighbor repulsion on the low frequency phase diagram of a quarter-filled Hubbard-Holstein chain
We have studied the influence of nearest-neighbor (NN) repulsion on the low
frequency phase diagram of a quarter-filled Hubbard-Holstein chain. The NN
repulsion term induces the apparition of two new long range ordered phases (one
CDW for positive and one CDW for
negative ) that did not exist in the V=0 phase diagram. These results
are put into perspective with the newly observed charge ordered phases in
organic conductors and an interpretation of their origin in terms of
electron-molecular vibration coupling is suggested.Comment: 10 pages, 10 figure
Detection of concealed accessory atrioventricular pathway by P-wave signal-averaged electrocardiogram
Coexisting orders in the quarter-filled Hubbard chain with elastic deformations
The electronic properties of the quarter-filled extended
Peierls-Holstein-Hubbard model that includes lattice distortions and molecular
deformations are investigated theoretically using the bosonization approach. We
predict the existence of a wide variety of charge-elastic phases depending of
the values of the Peierls and Holstein couplings. We include the effect of the
Peierls deformation in the nearest-neighbor repulsion V, that may be present in
real materials where Coulomb interactions depend strongly on the distance, and
we show that the phase diagram changes substantially for large V when this term
is taken into account.Comment: 6 pages, 3 figure
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