Mean-field approach to charge, orbital, and spin ordering in manganites

We present a mean-field theory of charge, orbital, and spin ordering in man ganites at 50% and 0% dopings, by considering Jahn-Teller interaction, near est-neighbor repulsion, and no single-site double occupancy. For spinless f ermions, we show that Jahn-Teller distortion and charge-orbital ordering oc cur simultaneously. In our two-dimensional model at 50% doping, for small n earest-neighbor repulsion the system is orbitally polarized while for large r repulsion the system undergoes CE type ordering. As for the 0% doping cas e, the ground state is orbitally antiferromagnetic. Upon including spin deg ree of freedom, at both 50% and 0% dopings the ordering remains the same at small antiferromagnetic coupling between adjacent core spins.