9,053 research outputs found
Dynamics of photoexcited states in one-dimensional dimerized Mott insulators
Dynamical properties of photoexcited states are theoretically studied in a
one-dimensional Mott insulator dimerized by the spin-Peierls instability.
Numerical calculations combined with a perturbative analysis have revealed that
the lowest photoexcited state without nearest-neighbor interaction corresponds
to an interdimer charge transfer excitation that belongs to dispersive
excitations. This excited state destabilizes the dimerized phase, leading to a
photoinduced inverse spin-Peierls transition. We discuss the purely electronic
origin of midgap states that are observed in a latest photoexcitation
experiment of an organic spin-Peierls compound, K-TCNQ
(potassium-tetracyanoquinodimethane).Comment: 13 pages, 13 figures, accepted for publication in PR
Photoinduced melting of charge order in a quarter-filled electron system coupled with different types of phonons
Photoinduced melting of charge order is calculated by using the exact
many-electron wave function coupled with classically treated phonons in the
one-dimensional quarter-filled Hubbard model with Peierls and Holstein types of
electron-phonon couplings. The model parameters are taken from recent
experiments on (EDO-TTF)_2PF_6 (EDO-TTF=ethylenedioxy-tetrathiafulvalene) with
(0110) charge order, where transfer integrals are modulated by molecular
displacements (bond-coupled phonons) and site energies by molecular
deformations (charge-coupled phonons). The charge-transfer photoexcitation from
(0110) to (0200) configurations and that from (0110) to (1010) configurations
have different energies. The corresponding excited states have different shapes
of adiabatic potentials as a function of these two phonon amplitudes. The
adiabatic potentials are shown to be useful in understanding differences in the
photoinduced charge dynamics and the efficiency of melting, which depend not
only on the excitation energy but also on the relative phonon frequency of the
bond- and charge-coupled phonons.Comment: 7 pages, 5 figures, accepted for publication in PR
Stable Optimization of a Tensor Product Variational State
We consider a variational problem for three-dimensional (3D) classical
lattice models. We construct the trial state as a two-dimensional product of
local variational weights that contain auxiliary variables. We propose a stable
numerical algorithm for the maximization of the variational partition function
per layer. The numerical stability and efficiency of the new method are
examined through its application to the 3D Ising model.Comment: 9 pages, 5 figures, in LaTex2e style. accepted for publication in
Prog. Theor. Phys. 11
Vertical Density Matrix Algorithm: A Higher-Dimensional Numerical Renormalization Scheme based on the Tensor Product State Ansatz
We present a new algorithm to calculate the thermodynamic quantities of
three-dimensional (3D) classical statistical systems, based on the ideas of the
tensor product state and the density matrix renormalization group. We represent
the maximum-eigenvalue eigenstate of the transfer matrix as the product of
local tensors which are iteratively optimized by the use of the ``vertical
density matrix'' formed by cutting the system along the transfer direction.
This algorithm, which we call vertical density matrix algorithm (VDMA), is
successfully applied to the 3D Ising model. Using the Suzuki-Trotter
transformation, we can also apply the VDMA to two-dimensional (2D) quantum
systems, which we demonstrate for the 2D transverse field Ising model.Comment: Unnecessary files are removed. 8 pages, 7 figures, submitted to
Phys.Rev.
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