9,236 research outputs found
Theory of Orbital Ordering, Fluctuation and Resonant X-ray Scattering in Manganites
A theory of resonant x-ray scattering in perovskite manganites is developed
by applying the group theory to the correlation functions of the pseudospin
operators for the orbital degree of freedom. It is shown that static and
dynamical informations of the orbital state are directly obtained from the
elastic, diffuse and inelastic scatterings due to the tensor character of the
scattering factor. We propose that the interaction and its anisotropy between
orbitals are directly identified by the intensity contour of the diffuse
scattering in the momentum space.Comment: 4 pages, 1 figur
Total reality of conormal bundles of hypersurfaces in almost complex manifolds
A generalization to the almost complex setting of a well-known result by S.
Webster is given. Namely, we prove that if is a strongly pseudoconvex
hypersurface in an almost complex manifold , then the conormal bundle
of is a totally real submanifold of (T^*M, \J), where \J is the
lifted almost complex structure on defined by Ishihara and Yano.Comment: 8 page
Spin and orbital excitation spectrum in the Kugel-Khomskii model
We discuss spin and orbital ordering in the twofold orbital degenerate
superexchange model in three dimensions relevant to perovskite transition metal
oxides. We focus on the particular point on the classical phase diagram where
orbital degeneracy is lifted by quantum effects exclusively. Dispersion and
damping of the spin and orbital excitations are calculated at this point taking
into account their mutual interaction. Interaction corrections to the
mean-field order parameters are found to be small. We conclude that
quasi-one-dimensional Neel spin order accompanied by the uniform
d_{3z^2-r^2}-type orbital ordering is stable against quantum fluctuations.Comment: 4 pages with 3 PS figures, 1 table, RevTeX, accepted to Phys. Rev. B.
Rapid Communicatio
Magnetic Ordering, Orbital Ordering and Resonant X-ray Scattering in Perovskite Titanates
The effective Hamiltonian for perovskite titanates is derived by taking into
account the three-fold degeneracy of orbitals and the strong
electron-electron interactions. The magnetic and orbital ordered phases are
studied in the mean-field approximation applied to the effective Hamiltonian. A
large degeneracy of the orbital states in the ferromagnetic phase is found in
contrast to the case of the doubly degenerate orbitals. Lifting of this
orbital degeneracy due to lattice distortions and spin-orbit coupling is
examined. A general form for the scattering cross section of the resonant x-ray
scattering is derived and is applied to the recent experimental results in
YTiO. The spin wave dispersion relation in the orbital ordered YTiO is
also studied.Comment: 10 pages, 6 figure
Ferromagnetic insulating phase in Pr{1-x}Ca{x}MnO3
A ferromagnetic insulating (FM-I) state in Pr0.75Ca0.25MnO3 has been studied
by neutron scattering experiment and theoretical calculation. The insulating
behavior is robust against an external magnetic field, and is ascribed to
neither the phase separation between a ferromagnetic metallic (FM-M) phase and
a non-ferromagnetic insulating one, nor the charge ordering. We found that the
Jahn-Teller type lattice distortion is much weaker than PrMnO3 and the magnetic
interaction is almost isotropic. These features resembles the ferromagnetic
metallic state of manganites, but the spin exchange interaction J is much
reduced compared to the FM-M state. The theoretical calculation based on the
staggered type orbital order well reproduces several features of the spin and
orbital state in the FM-I phase.Comment: REVTeX4, 10 pages, 9 figure
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
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