5,805 research outputs found

### Photoinduced coherent oscillations in the one-dimensional two-orbital Hubbard model

We study photoinduced ultrafast coherent oscillations originating from
orbital degrees of freedom in the one-dimensional two-orbital Hubbard model. By
solving the time-dependent Schr\"odinger equation for the numerically exact
many-electron wave function, we obtain time-dependent optical response
functions. The calculated spectra show characteristic coherent oscillations
that vary with the frequency of probe light. A simple analysis for the dominant
oscillating components clarifies that these photoinduced oscillations are
caused by the quantum interference between photogenerated states. The
oscillation attributed to the Raman-active orbital excitations (orbitons)
clearly appears around the charge-transfer peak.Comment: 5 pages, 5 figure

### Frustration-induced eta inversion in the S=1/2 bond-alternating spin chain

We study the frustration-induced enhancement of the incommensurate
correlation for a bond-alternating quantum spin chain in a magnetic field,
which is associated with a quasi-one-dimensional organic compound F5PNN. We
investigate the temperature dependence of the staggered susceptibilities by
using the density matrix renormalization group, and then find that the
incommensurate correlation becomes dominant in a certain range of the magnetic
field. We also discuss the mechanism of this enhancement on the basis of the
mapping to the effective S=1/2 XXZ chain and a possibility of the field-induced
incommensurate long range order.Comment: 4 pages, 5 figures, replaced with revised version accepted to PR

### Charge-Transfer Excitations in One-Dimensional Dimerized Mott Insulators

We investigate the optical properties of one-dimensional (1D) dimerized Mott
insulators using the 1D dimerized extended Hubbard model. Numerical
calculations and a perturbative analysis from the decoupled-dimer limit clarify
that there are three relevant classes of charge-transfer (CT) states generated
by photoexcitation: interdimer CT unbound states, interdimer CT exciton states,
and intradimer CT exciton states. This classification is applied to
understanding the optical properties of an organic molecular material,
1,3,5-trithia-2,4,6-triazapentalenyl (TTTA), which is known for its
photoinduced transition from the dimerized spin-singlet phase to the regular
paramagnetic phase. We conclude that the lowest photoexcited state of TTTA is
the interdimer CT exciton state and the second lowest state is the intradimer
CT exciton state.Comment: 6 pages, 6 figures, to be published in J. Phys. Soc. Jp

### Fractional S^z excitation and its bound state around the 1/3 plateau of the S=1/2 Ising-like zigzag XXZ chain

We present the microscopic view for the excitations around the 1/3 plateau
state of the Ising-like zigzag XXZ chain. We analyze the low-energy excitations
around the plateau with the degenerating perturbation theory from the Ising
limit, combined with the Bethe-form wave function. We then find that the
domain-wall particles carrying $S^z=\pm 1/3$ and its bound state of $S^z=\pm
2/3$ describe well the low-energy excitations around the 1/3 plateau state. The
formation of the bound state of the domain-walls clearly provides the
microscopic mechanism of the cusp singularities and the even-odd behavior in
the magnetization curve.Comment: 13 pages, 15 figure

### Photoinduced charge and spin dynamics in strongly correlated electron systems

Motivated by photoinduced phase transition in manganese oxides, charge and
spin dynamics induced by photoirradiation are examined. We calculate the
transient optical absorption spectra of the extended double-exchange model by
the density matrix renormalization group (DMRG) method. A charge-ordered
insulating (COI) state becomes metallic just after photoirradiation, and the
system tends to recover the initial COI state. The recovery is accompanied with
remarkable suppression of an antiferromagnetic correlation in the COI state.
The DMRG results are consistent with recent pump-probe spectroscopy data.Comment: 5 pages, 4 figure

### Production of Kaluza-Klein States at Future Colliders

Perturbative breaking of supersymmetry in four-dimensional string theories
predict in general the existence of new large dimensions at the TeV scale. Such
large dimensions lie in a domain of energies accessible to particle
accelerators. Their main signature is the production of Kaluza-Klein
excitations which can be detected at future colliders. We study this
possibility for hadron colliders (TEVATRON, LHC) and $e^+ e^-$ colliders
(LEP-200, NLC-500).Comment: 13 pages, LATEX, 4 postscript figures appended at the end,
CPTH-A293.0294 and IEM-FT-84/9

### Magnetic phase diagram of the S=1/2 antiferromagnetic zigzag spin chain in the strongly frustrated region: cusp and plateau

We determine the magnetic phase diagram of the antiferromagnetic(AF) zigzag
spin chain in the strongly frustrated region, using the density matrix
renormalization group method. We find the magnetization plateau at 1/3 of the
full moment accompanying the spontaneous symmetry breaking of the translation,
the cusp singularities above and/or below the plateau, and the even-odd effect
in the magnetization curve. We also discuss the formation mechanisms of the
plateau and cusps briefly.Comment: 4 pages, 8 figures, revised version, to appear in J.Phys.Soc.Jp

### Self-Consistent Tensor Product Variational Approximation for 3D Classical Models

We propose a numerical variational method for three-dimensional (3D)
classical lattice models. We construct the variational state as a product of
local tensors, and improve it by use of the corner transfer matrix
renormalization group (CTMRG), which is a variant of the density matrix
renormalization group (DMRG) applied to 2D classical systems. Numerical
efficiency of this approximation is investigated through trial applications to
the 3D Ising model and the 3D 3-state Potts model.Comment: 12 pages, 6 figure

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