1,522 research outputs found
Numerical Study of Photo-Induced Dynamics in Double-Exchange Model
Photo-induced spin and charge dynamics in double-exchange model are
numerically studied. The Lanczos method and the density-matrix
renormalization-group method are applied to one-dimensional finite-size
clusters. By photon irradiation in a charge ordered (CO) insulator associated
with antiferromagnetic (AFM) correlation, both the CO and AFM correlations
collapse rapidly, and appearances of new peaks inside of an insulating gap are
observed in the optical spectra and the one-particle excitation spectra. Time
evolutions of the spin correlation and the in-gap state are correlated with
each other, and are governed by the transfer integral of conduction electrons.
Results are interpreted by the charge kink/anti-kink picture and their
effective motions which depend on the localized spin correlation. Pump-photon
density dependence of spin and charge dynamics are also studied. Roles of spin
degree of freedom are remarkable in a case of weak photon density. Implications
of the numerical results for the pump-probe experiments in perovskite
manganites are discussed.Comment: 16 pages, 16 figure
Photoinduced magnetic bound state in itinerant correlated electron system with spin-state degree of freedom
Photo-excited state in correlated electron system with spin-state degree of
freedom is studied. We start from the two-orbital extended Hubbard model where
energy difference between the two orbitals is introduced. Photo-excited
metastable state is examined based on the effective model Hamiltonian derived
by the two-orbital Hubbard model. Spin-state change is induced by
photo-irradiation in the low-spin band insulator near the phase boundary.
High-spin state is stabilized by creating a ferromagnetic bound state with
photo-doped hole carriers. An optical absorption occurs between the bonding and
antibonding orbitals inside of the bound state. Time-evolution for
photo-excited states is simulated in the time-dependent mean-field scheme.
Pair-annihilations of the photo-doped electron and hole generate the high-spin
state in a low-spin band insulator. We propose that this process is directly
observed by the time-resolved photoemission experiments.Comment: 15 pages, 16 figure
What is the true charge transfer gap in parent insulating cuprates?
A large body of experimental data point towards a charge transfer instability
of parent insulating cuprates to be their unique property. We argue that the
true charge transfer gap in these compounds is as small as 0.4-0.5\,eV rather
than 1.5-2.0\,eV as usually derived from the optical gap measurements. In fact
we deal with a competition of the conventional (3d) ground state and a
charge transfer (CT) state with formation of electron-hole dimers which evolves
under doping to an unconventional bosonic system. Our conjecture does provide
an unified standpoint on the main experimental findings for parent cuprates
including linear and nonlinear optical, Raman, photoemission, photoabsorption,
and transport properties anyhow related with the CT excitations. In addition we
suggest a scenario for the evolution of the CuO planes in the CT unstable
cuprates under a nonisovalent doping.Comment: 13 pages, 5 figures, submitted to PR
Orbital Compass Model as an Itinerant Electron System
Two-dimensional orbital compass model is studied as an interacting itinerant
electron model. A Hubbard-type tight-binding model, from which the orbital
compass model is derived in the strong coupling limit, is identified. This
model is analyzed by the random-phase approximation (RPA) and the
self-consistent RPA methods from the weak coupling. Anisotropy for the orbital
fluctuation in the momentum space is qualitatively changed by the on-site
Coulomb interaction. This result is explained by the fact that the dominant
fluctuation is changed from the intra-band nesting to the inter-band one by
increasing the interaction.Comment: 7 pages, 8 figure
Real-space observation of current-driven domain wall motion in submicron magnetic wires
Spintronic devices, whose operation is based on the motion of a magnetic
domain wall (DW), have been proposed recently. If a DW could be driven directly
by flowing an electric current instead of a magnetic field, the performance and
functions of such device would be drastically improved. Here we report
real-space observation of the current-driven DW motion by using a well-defined
single DW in a micro-fabricated magnetic wire with submicron width. Magnetic
force microscopy (MFM) visualizes that a single DW introduced in the wire is
displaced back and forth by positive and negative pulsed-current, respectively.
We can control the DW position in the wire by tuning the intensity, the
duration and the polarity of the pulsed-current. It is, thus, demonstrated that
spintronic device operation by the current-driven DW motion is possible.Comment: Accepted and published in PR
Coherent dynamics of photoinduced nucleation processes
We study the dynamics of initial nucleation processes of photoinduced
structural change of molecular crystals. In order to describe the nonadiabatic
transition in each molecule, we employ a model of localized electrons coupled
with a fully quantized phonon mode, and the time-dependent Schr\"odinger
equation for the model is numerically solved. We found a minimal model to
describe the nucleation induced by injection of an excited state of a single
molecule in which multiple types of intermolecular interactions are required.
In this model coherently driven molecular distortion plays an important role in
the successive conversion of electronic states which leads to photoinduced
cooperative phenomena.Comment: 14 pages, 5 figure
Propagation of a magnetic domain wall in magnetic wires with asymmetric notches
The propagation of a magnetic domain wall (DW) in a submicron magnetic wire
consisting of a magnetic/nonmagnetic/magnetic trilayered structure with
asymmetric notches was investigated by utilizing the giant magnetoresistance
effect. The propagation direction of a DW was controlled by a pulsed local
magnetic field, which nucleates the DW at one of the two ends of the wire. It
was found that the depinning field of the DW from the notch depends on the
propagation direction of the DW.Comment: 12 pages, 3 figure
Electronic structure and electric-field gradients analysis in
Electric field gradients (EFG's) were calculated for the compound at
both and sites. The calculations were performed within
the density functional theory (DFT) using the augmented plane waves plus local
orbital (APW+lo) method employing the so-called LDA+U scheme. The
compound were treated as nonmagnetic, ferromagnetic, and antiferromagnetic
cases. Our result shows that the calculated EFG's are dominated at the
site by the Ce-4f states. An approximately linear relation is
intuited between the main component of the EFG's and total density of states
(DOS) at Fermi level. The EFG's from our LDA+U calculations are in better
agreement with experiment than previous EFG results, where appropriate
correlations had not been taken into account among 4f-electrons. Our result
indicates that correlations among 4f-electrons play an important role in this
compound and must be taken into account
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