291 research outputs found
Spin and charge ordering in self-doped Mott insulators
We have investigated possible spin and charge ordered states in 3d
transition-metal oxides with small or negative charge-transfer energy, which
can be regarded as self-doped Mott insulators, using Hartree-Fock calculations
on d-p-type lattice models. It was found that an antiferromagnetic state with
charge ordering in oxygen 2p orbitals is favored for relatively large
charge-transfer energy and may be relevant for PrNiO and NdNiO. On the
other hand, an antiferromagnetic state with charge ordering in transition-metal
3 orbitals tends to be stable for highly negative charge-transfer energy and
can be stabilized by the breathing-type lattice distortion; this is probably
realized in YNiO.Comment: 4 pages, 4 figure
Interplay between orbital ordering and lattice distortions in LaMnO3, YVO3, and YTiO3
We have studied the interplay between orbital ordering, Jahn-Teller and
GdFeO3-type lattice distortions in perovskite-type transition-metal oxides
using model Hartree-Fock calculations. It has been found that the covalency
between A-site cations and oxygens causes interaction between the Jahn-Teller
and GdFeO3-type distortions. The present calculations explain why the d-type
Jahn-Teller distortion and orbital ordering compatible with it are realized in
LaMnO3, YVO3 and YTiO3Comment: 5 pages, 8 figure
Electronic structure of InMnAs studied by photoemission spectroscopy: Comparison with GaMnAs
We have investigated the electronic structure of the -type diluted
magnetic semiconductor InMnAs by photoemission spectroscopy. The Mn
3 partial density of states is found to be basically similar to that of
GaMnAs. However, the impurity-band like states near the top of
the valence band have not been observed by angle-resolved photoemission
spectroscopy unlike GaMnAs. This difference would explain the
difference in transport, magnetic and optical properties of
InMnAs and GaMnAs. The different electronic
structures are attributed to the weaker Mn 3 - As 4 hybridization in
InMnAs than in GaMnAs.Comment: 4 pages, 3 figure
Orbital polarons and ferromagnetic insulators in manganites
We argue that in lightly hole doped perovskite-type Mn oxides the holes
(Mn sites) are surrounded by nearest neighbor Mn sites in which
the occupied orbitals have their lobes directed towards the central hole
(Mn) site and with spins coupled ferromagnetically to the central spin.
This composite object, which can be viewed as a combined orbital-spin-lattice
polaron, is accompanied by the breathing type (Mn) and Jahn-Teller type
(Mn) local lattice distortions. We present calculations which indicate
that for certain doping levels these orbital polarons may crystallize into a
charge and orbitally ordered ferromagnetic insulating state.Comment: 5 pages, 4 figures, to be published in PR
Electron-lattice coupling, orbital stability and the phase diagram of CaSrRuO
Hartree-Fock calculations are presented of a theoretical model describing the
Sr/CaRuO family of compounds. Both commensurate and incommensurate magnetic
states are considered, along with orbital ordering and the effect of lattice
distortions. For reasonable parameter values, interactions disfavor orbital
disproportionation. A coherent description of the observed phase diagram is
obtained.Comment: Changed content, and added a new referenc
Charge and orbital ordering in underdoped La1-xSrxMnO3
We have explored spin, charge and orbitally ordered states in La1-xSrxMnO3 (0
< x < 1/2) using model Hartree-Fock calculations on d-p-type lattice models. At
x=1/8, several charge and orbitally modulated states are found to be stable and
almost degenerate in energy with a homogeneous ferromagnetic state. The present
calculation indicates that a ferromagnetic state with a charge modulation along
the c-axis which is consistent with the experiment by Yamada et al. might be
responsible for the anomalous behavior around x = 1/8.Comment: 5 pages, 5 figure
Coexistence of localized and itinerant electrons in BaFe2X3 (X = S and Se) revealed by photoemission spectroscopy
We report a photoemission study at room temperature on BaFe2X3 (X = S and Se)
and CsFe2Se3 in which two-leg ladders are formed by the Fe sites. The Fe 2p
core-level peaks of BaFe2X3 are broad and exhibit two components, indicating
that itinerant and localized Fe 3d sites coexist similar to KxFe2-ySe2. The Fe
2p core-level peak of CsFe2Se3 is rather sharp and is accompanied by a
charge-transfer satellite. The insulating ground state of CsFe2Se3 can be
viewed as a Fe2+ Mott insulator in spite of the formal valence of +2.5. The
itinerant versus localized behaviors can be associated with the stability of
chalcogen p holes in the two-leg ladder structure.Comment: 5 pages, 5 figures, Accepted in publication for Physical Review
Prediction of Orbital Ordering in Single-Layered Ruthenates
The key role of the orbital degree of freedom to understand the magnetic
properties of layered ruthenates is here discussed. In the G-type
antiferromagnetic phase of CaRuO, recent X-ray experiments reported the
presence of 0.5 hole per site in the orbital, while the
and orbitals contain 1.5 holes. This unexpected hole
distribution is explained by a novel state with orbital ordering (OO),
stabilized by a combination of Coulomb interactions and lattice distortions. In
addition, the rich phase diagram presented here suggests the possibility of
large magnetoresistance effects, and predicts a new ferromagnetic OO phase in
ruthenates.Comment: 4 pages, Revtex, with 2 figures embedded in the text. Submitted to
Phys. Rev. Let
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