相关论文: Double exchange model for correlated electrons in …
We investigate the role of the double exchange mechanism for stability of the metallic C-type antiferromagnetic (C-AF) phase, which was observed experimentally in hole doped La$_{1-x}$Sr$_x$VO$_3$. The double exchange model treats localized…
We consider the double-exchange for systems in which doped electrons occupy degenerate orbitals, treating the realistic situation with double degenerate $e_g$ orbitals. We show that the orbital degeneracy leads in general to formation of…
We investigate the role of orbital degeneracy in the double exchange (DE) model. In the $J_{H}\to\infty$ limit, an effective generalized ``Hubbard'' model incorporating orbital pseudospin degrees of freedom is derived. The model possesses…
We study a model for orbitally degenerate Mott insulators, where localized electrons possess t_2g degrees of freedom coupled by several, competing, exchange mechanisms. We provide evidence for two distinct strongly fluctuating regimes,…
A double exchange model for degenerate $e_g$ orbitals with intra- and inter-orbital interactions has been studied for the electron doped manganites A$_{1-x}$B$_{x}$MnO$_3$ ($x > 0.5$). We show that such a model reproduces the observed phase…
We explore mechanisms of orbital order decay in doped Mott insulators $R_{1-x}$(Sr,Ca)$_x$VO$_3$ ($R=\,$Pr,Y,La) caused by charged (Sr,Ca) defects. Our unrestricted Hartree-Fock analysis focuses on the combined effect of random, charged…
We have analyzed the symmetry properties and the ground state of an orbital Hubbard model with two orbital flavors, describing a partly filled spin-polarized $e_g$ band on a cubic lattice, as in ferromagnetic manganites. We demonstrate that…
We present our theoretical results on an effective two-band double-exchange model on a pyrochlore lattice for understanding intricate phase competition in Mo pyrochlore oxides. The model includes the twofold degeneracy of $e_g'$ orbitals…
Orbitally degenerate systems provide a promising platform for realizing novel quantum phases driven by spin-orbital exchange interactions, as described by the Kugel-Khomskii model. Spinel vanadates, in which orbital degrees of freedom…
We analyze the role of orbital degeneracy in possible magnetic and orbital instabilities by solving exactly a two-site molecule with two orbitals of either $e_g$ or $t_{2g}$ symmetry at quarter-filling. As a generic feature of both models…
We summarize some characteristic features of the frustrated magnetic interactions in spin-orbital models adequate for cubic transition metal oxides with orbital degeneracy. A generic tendency towards dimerization, found already in the…
We study the ferromagnetism due to orbital degeneracy in the Hubbard model in infinite dimensions. The model contains the intraorbital repulsion $U$, the interorbital repulsion $U^\prime$, the exchange $J$ (Hund coupling) and the pair…
Ring-exchange (RE) interaction in Mott insulator with doubly degenerate $e_g$ orbitals is studied. Hamiltonian for the RE interaction is derived by the perturbational calculation. A remarkably weak RE interaction destroys the orbital order…
Taking the orbital degeneracy of $e_g$ conduction bands and the Coulomb interaction into account in a double-exchange model, we investigate charge dynamics of perovskite Mn oxides by the Lancz$\ddot{\rm o}$s diagonalization method. In the…
We start from an effective Hamiltonian for Ru ions in a square lattice, which includes the on-site interactions between t_2g orbitals derived from Coulomb repulsion, and a tetragonal crystal-field splitting. Using perturbation theory in the…
Phase diagram of half-doped perovskite manganites is studied within the extended double-exchange model. To demonstrate the role of orbital degrees of freedom both one- and two-orbital models are examined. A rich phase diagram is obtained in…
A possible mechanism of electronic phase separation in the systems with orbital ordering is analyzed. We suggest a simple model taking into account an interplay between the delocalization of charge carriers introduced by doping and the…
We investigate the spectral properties of a hole moving in a two-dimensional Hubbard model for strongly correlated t_2g electrons. Although superexchange interactions are Ising-like, a quasi-one-dimensional coherent hole motion arises due…
We study the effective spin-orbital model derived for the d9 ions in a three-dimensional perovskite lattice, as in KCuF_3, where at each site the doubly degenerate eg orbitals contain a single hole. The model describes the superexchange…
We start from a six-band model describing the transition-metal t2g orbitals of half-metallic double perovskite systems, such as Sr2FeMoO6, in which only one of the transition metal ions (Fe) contains important intratomic repulsion Ufe. By…