Anti-Jahn-Teller polaron in ${\mathrm{LaMnO}}_3$

Distortions of the oxygen sublattice couple to $e_g$ orbitals of ${\mathrm{Mn}}^{3+}$ and drive a cooperative Jahn-Teller (orbital ordering) transition in ${\mathrm{LaMnO}}_3.$ A simple model for this transition is studied. Without further adjustment, the model predicts the shape and stability of small (anti-Jahn-Teller) polarons that form when holes are doped into the material. This leads to a new description of the lightly-doped insulator, the antiferromagnetic to ferromagnetic transition, and the metal-insulator transition.