7,632 research outputs found
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
BIRC2 (baculoviral IAP repeat-containing 2)
Review on BIRC2 (baculoviral IAP repeat-containing 2), with data on DNA, on the protein encoded, and where the gene is implicated
Polarized far-infrared and Raman spectra of SrCuO2 single crystals
We measured polarized far-infrared reflectivity and Raman scattering spectra
of SrCuO single crystals. The frequencies for infrared-active modes were
determined using an oscillator-fitting procedure of reflectivity data. The
Raman spectra were measured at different temperatures using several laser
energies . In addition to eight of twelve Raman active modes,
predicted by factor-group analysis, we observed a complex structure in the
Raman spectra for polarization parallel to the {\bf c}-axis, which consists of
Raman-allowed A symmetry modes, and B LO infrared-active
(Raman-forbidden) modes of the first and higher order as well as their
combinations. The Raman-forbidden modes have a stronger intensity at higher
than the Raman-allowed ones. In order to explain this resonance
effect, we measured the dielectric function and optical reflection spectra of
SrCuO in the visible range. We show that the Raman-allowed A symmetry
modes are resonantly enhanced when a laser energy is close to , while
Raman-forbidden (IR-active) modes resonate strongly for laser line energies
close to the electronic transition of higher energy gaps.Comment: to be published in Physica
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
Symmetry adapted finite-cluster solver for quantum Heisenberg model in two-dimensions: a real-space renormalization approach
We present a quantum cluster solver for spin- Heisenberg model on a
two-dimensional lattice. The formalism is based on the real-space
renormalization procedure and uses the lattice point group-theoretical analysis
and nonabelian SU(2) spin symmetry technique. The exact diagonalization
procedure is used twice at each renormalization group step. The method is
applied to the spin-half antiferromagnet on a square lattice and a calculation
of local observables is demonstrated. A symmetry based truncation procedure is
suggested and verified numerically.Comment: willm appear in J. Phys.
The Protein Storage Vacuole: A Unique Compound Organelle
doi: 10.1083/jcb.200107012Storage proteins are deposited into protein storage vacuoles (PSVs) during plant seed development and maturation and stably accumulate to high levels; subsequently, during germination the storage proteins are rapidly degraded to provide nutrients for use by the embryo. Here, we show that a PSV has within it a membrane-bound compartment containing crystals of phytic acid and proteins that are characteristic of a lytic vacuole. This compound organization, a vacuole within a vacuole whereby storage functions are separated from lytic functions, has not been described previously for organelles within the secretory pathway of eukaryotic cells. The partitioning of storage and lytic functions within the same vacuole may reflect the need to keep the functions separate during seed development and maturation and yet provide a ready source of digestive enzymes to initiate degradative processes early in germination.This work was supported by grants from the National Science Foundation (MCB-9974429), Department of Energy (DE-FG03-97ER20277), and Human
Frontier Science Program (RG0018/2000) to J.C. Rogers, and from the Department of Energy (DE-FG02-91ER20055) to P.A. Rea. Y.M. Drozdowicz is an NSF/DOE/USDA Plant Training Grant fellow. L. Jiang is supported by a Direct Grant (project code 2030238) and a Special Grant for Conducting
Research Abroad in the Summer of 2001 from the Chinese University
of Hong Kong, and a grant from the Research Grants Council of the
Hong Kong Special Administrative Region, China (project CUHK4156/
01M)
Application of the density matrix renormalization group method to finite temperatures and two-dimensional systems
The density matrix renormalization group (DMRG) method and its applications
to finite temperatures and two-dimensional systems are reviewed. The basic idea
of the original DMRG method, which allows precise study of the ground state
properties and low-energy excitations, is presented for models which include
long-range interactions. The DMRG scheme is then applied to the diagonalization
of the quantum transfer matrix for one-dimensional systems, and a reliable
algorithm at finite temperatures is formulated. Dynamic correlation functions
at finite temperatures are calculated from the eigenvectors of the quantum
transfer matrix with analytical continuation to the real frequency axis. An
application of the DMRG method to two-dimensional quantum systems in a magnetic
field is demonstrated and reliable results for quantum Hall systems are
presented.Comment: 33 pages, 18 figures; corrected Eq.(117
Excitation Spectrum of One-dimensional Extended Ionic Hubbard Model
We use Perturbative Continuous Unitary Transformations (PCUT) to study the
one dimensional Extended Ionic Hubbard Model (EIHM) at half-filling in the band
insulator region. The extended ionic Hubbard model, in addition to the usual
ionic Hubbard model, includes an inter-site nearest-neighbor (n.n.) repulsion,
. We consider the ionic potential as unperturbed part of the Hamiltonian,
while the hopping and interaction (quartic) terms are treated as perturbation.
We calculate total energy and ionicity in the ground state. Above the ground
state, (i) we calculate the single particle excitation spectrum by adding an
electron or a hole to the system. (ii) the coherence-length and spectrum of
electron-hole excitation are obtained. Our calculations reveal that for V=0,
there are two triplet bound state modes and three singlet modes, two anti-bound
states and one bound state, while for finite values of there are four
excitonic bound states corresponding to two singlet and two triplet modes. The
major role of on-site Coulomb repulsion is to split singlet and triplet
collective excitation branches, while tends to pull the singlet branches
below the continuum to make them bound states.Comment: 10 eps figure
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