Resumo
Understanding orbital ordered (OO) Mott insulating states lies at the heart of a consistent resolution of the colossal magneto-resistance (CMR) observed in manganites, where its melting induces a low-T insulator-metal transition upon hole doping for 0.25 ≤ x ≤ 0.45. Motivated thereby, we study the OO states in a planar model for bilayer manganites using dynamical-mean-field-theory (DMFT) and finite-size diagonalisation methods. We derive the OO ground states in manganites, for x = 0, 2 1 , 3 2 , 34 in agreement with observations, including the charge-orbital-magnetic ordered stripe phases for x > 12 . These OO states are shown to be associated with an alloy ordering of the d 3x 2 −r 2 /d 3y 2 −r 2 orbitals on each Mn 3+ site.
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