Orbital polarons and ferromagnetic insulators in manganites

We argue that in lightly hole doped perovskite-type Mn oxides the holes $({\mathrm{Mn}}^{4+}$ sites) are surrounded by nearest neighbor ${\mathrm{Mn}}^{3+}$ sites in which the occupied $3d$ orbitals have their lobes directed towards the central hole $\left({\mathrm{Mn}}^{4+}\right)$ 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 $\left({\mathrm{Mn}}^{4+}\right)$ and Jahn-Teller type $\left({\mathrm{Mn}}^{3+}\right)$ 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.