460 research outputs found
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
Role of Orbital Degeneracy in Double Exchange Systems
We investigate the role of orbital degeneracy in the double exchange (DE)
model. In the limit, an effective generalized ``Hubbard''
model incorporating orbital pseudospin degrees of freedom is derived. The model
possesses an exact solution in one- and in infinite dimensions. In 1D, the
metallic phase off ``half-filling'' is a Luttinger liquid with
pseudospin-charge separation. Using the solution for our effective
model, we show how many experimental observations for the well-doped () three-dimensional manganites can be qualitatively
explained by invoking the role of orbital degeneracy in the DE model.Comment: 8 pages, 2 figures, submitted to Phys. Rev.
Transition between two ferromagnetic states driven by orbital ordering in La_{0.88}Sr_{0.12}MnO_3
A lightly doped perovskite mangantite La_{0.88}Sr_{0.12}MnO_3 exhibits a
phase transition at T_{OO}=145 K from a ferromagnetic metal (T_C=172 K) to a
novel ferromagnetic insulator.We identify that the key parameter in the
transition is the orbital degree of freedom in e_g electrons. By utilizing the
resonant x-ray scattering technique, orbital ordering is directly detected
below T_{OO}, in spite of a significant diminution of the cooperative
Jahn-Teller distortion. The new experimental features are well described by a
theory treating the orbital degree of freedom under strong electron
correlation. The present experimental and theoretical studies uncover a crucial
role of the orbital degree in the metal-insulator transition in lightly doped
manganites.Comment: 4 pages, 4 figure
Phase Transition in Perovskite Manganites with Orbital Degree of Freedom
Roles of orbital degree of freedom of Mn ions in phase transition as a
function of temperature and hole concentration in perovskite manganites are
studied. It is shown that the orbital order-disorder transition is of the first
order in the wide region of hole concentration and the Nel
temperature for the anisotropic spin ordering, such as the layer-type
antiferromagnetic one, is lower than the orbital ordering temperature due to
the anisotropy in the orbital space. The calculated results of the temperature
dependence of the spin and orbital order parameters explain a variety of the
experiments observed in manganites.Comment: 10 pages, 5 figure
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