Related papers: Orbital Order, Stripe Phases and Mott Transition i…
Large scale Monte Carlo simulation results for the two-orbital model for manganites, including Jahn-Teller lattice distortions, are here presented. At hole density x=1/4 and in the vicinity of the region of competition between the…
We investigated the temperature ($T=$ 15 $\sim $ 290 K) and the magnetic field ($H=$ 0 $\sim $ 17 T) dependent optical conductivity spectra of a charge/orbital ordered manganite, Nd$_{1/2}$Sr$_{1/2}$MnO$_3$. With variation of $T$ and $H$,…
An orbital ordering, often observed in Mott insulators with orbital degeneracy, is usually supposed to disappear with doping, e.g. in the ferromagnetic metallic phase of manganites. We propose that the orbital ordering of a novel type may…
Spin-charge-orbital ordered structures in doped layered manganites are investigated using an orbital-degenerate double-exchange model tightly coupled to Jahn-Teller distortions. In the ferromagnetic phase, unexpected diagonal stripes at…
The magnetic and orbital orders for the bilayer manganites in the doping region $0.5 < x <1.0$ have been investigated from a model that incorporates the two $e_g$ orbitals at each Mn site, the inter-orbital Coulomb interaction and lattice…
Correlation between orbital structure and magnetic ordering in bilayered manganites is examined. A level separation between the $3d_{3z^2-r^2}$ and $3d_{x^2-y^2}$ orbitals in a Mn ion is calculated in the ionic model for a large number of…
A short introduction to the complex phenomena encountered in transition metal oxides with either charge or orbital or joint charge-and-orbital order, usually accompanied by magnetic order, is presented. It is argued that all the types of…
The phase diagrams of LaMnO$_3$ perovskites have been intensely studied due to the colossal magnetoresistance (CMR) exhibited by compositions around the $\frac{3}{8}^{th}$ doping level. However, phase segregation between ferromagnetic (FM)…
We consider the orbital ordering in LaMnO3 and similar systems, proceeding from the band picture. We show that for the realistic magnetic structure of A-type there exists a complete nesting betweeen two e_g-bands. As a result there occurs…
We investigate the high temperature phase of layered manganites, and demonstrate that the charge-orbital phase transition without magnetic order in La$_{0.5}$Sr$_{1.5}$MnO$_4$ can be understood in terms of the density wave instability. The…
We report the observation of superstructures associated with the oxygen 2p-states in two prototypical manganites using x-ray diffraction at the oxygen K-edge. We determine the nature of the orderings and discuss our picture with respect to…
There have been recent reports of charge ordering around $x=0.5$ in the bilayer manganites. At $x=0.5$, there appears to be a coexistence region of layered A-type antiferromagnetc and charge order. There are also reports of orbital order in…
The crystallographic and magnetic phase diagram of the n=2 layered manganite La2-2xSr1+2xMn2O7 in the region x=>0.5 has been studied using temperature dependent neutron powder diffraction. The magnetic phase diagram reveals a progression of…
Basic mechanisms controlling orbital order and orbital fluctuations in transition metal oxides are discussed. The lattice driven classical orbital picture, e.g. like in manganites LaMnO$_3$, is contrasted to the quantum behavior of orbitals…
A systematic study of the electronic structure in perovskite manganites is presented. The effective Hamiltonian is derived by taking into account the degeneracy of $e_g$ orbitals and strong electron correlation in Mn ions. The spin and…
We demonstrate that the half-doped bilayer manganite La_{1}Sr_{2}Mn_{2}O_{7} exhibits CE-type charge-ordered and spin-ordered states below $T_{N, CO}^A = 210$ K and below $T_{N}^{CE} \sim 145$ K, respectively. However, the volume fraction…
We present evidence that the insulator to metal transition in (La,Ca)MnO3 near x~0.2 is driven by the suppression of coherent Jahn-Teller distortions, originating from d type orbital ordering. The orbital ordered state is characterised by…
The charge ordering in the bilayer manganite system La$_{2-2x}$Sr$_{1+2x}$Mn$_{2}$O$_{7}$ with $0.30 \le x \le 0.50$ has been studied by neutron diffraction. The charge order is characterized by the propagation vector parallel to the [1 0…
Spin, charge, and orbital structures in models for doped manganites are studied by a combination of analytic mean-field and numerical relaxation techniques. At realistic values for the electron-phonon and antiferromagnetic $t_{2g}$ spin…
We use exact diagonalization combined with mean-field theory to investigate the phase diagram of the spin-orbital model for cubic vanadates. The spin-orbit coupling competes with Hund's exchange and triggers a novel phase, with the ordering…