926 research outputs found
Interchain coupling effects on photoinduced phase transitions between neutral and ionic phases in an extended Hubbard model with alternating potentials and an electron-lattice coupling
Dynamics of ionic-to-neutral and neutral-to-ionic phase transitions induced
by intrachain charge-transfer photoexcitations are studied in a
quasi-one-dimensional extended Hubbard model with alternating potentials and an
electron-lattice coupling for mixed-stack charge-transfer complexes. For
interchain couplings, we use electron-electron interactions previously
estimated for TTF-CA (TTF=tetrathiafulvalene, CA=chloranil). Photoexcitation is
introduced by a pulse of oscillating electric field. The time-dependent
Hartree-Fock approximation is used for the electronic part, and the classical
approximation for the lattice part. In the ionic-to-neutral transition, the
transferred charge density is a strongly nonlinear function of the
photoexcitation density, which is characterized by the presence of a threshold.
With substantial interchain couplings comparable to those in TTF-CA, the
interchain correlation is strong during the transition. Neutral domains in
nearby chains simultaneously grow even if their nucleation is delayed by
reducing the amplitude of the electric field. With weaker interchain couplings,
the growing processes are in phase only when the amplitude of the electric
field is large. Thus, the experimentally observed, coherent motion of a
macroscopic neutral-ionic domain boundary is allowed to emerge by such
substantial interchain couplings. In the neutral-to-ionic transition, by
contrast, the transferred charge density is almost a linear function of the
photoexcitation density. Interchain electron-electron interactions make the
function slightly nonlinear, but the uncooperative situation is almost
unchanged and consistent with the experimental findings.Comment: 8 pages, 7 figures, to appear in Phys. Rev.
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
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
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