Spin-orbital order in LaMnO3 : d−p model study

Using the multiband $d\ensuremath{-}p$ model and unrestricted Hartree-Fock approximation, we investigate the electronic structure and spin-orbital order in three-dimensional ${\mathrm{MnO}}_{3}$ lattice such as realized in ${\mathrm{LaMnO}}_{3}$. The orbital order is induced and stabilized by particular checkerboard pattern of oxygen distortions arising from the Jahn-Teller effect in the presence of strong Coulomb interactions on ${e}_{g}$ orbitals of Mn ions. We show that the spin-orbital order can be modeled using a simple Ansatz for local crystal fields alternating between two sublattices on Mn ions, which have nonequivalent neighboring oxygen distortions in $ab$ planes. The simple and computationally very inexpensive $d\ensuremath{-}p$ model reproduces correctly nontrivial spin-orbital order observed in undoped ${\mathrm{LaMnO}}_{3}$. Orbital order is very robust and is reduced by $\ensuremath{\sim}3$ % for large self-doping in the metallic regime.