Orbital polarons and ferromagnetic insulators in manganites

Abstract

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

5 pages, 4 figures, to be published in PRB

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