Observation of orbital ordering and Jahn-Teller distortions supporting the Wigner-crystal model in highly doped Bi1- xCaxMnO3

We report on the experimental characterization of orbital ordering and the associated lattice distortions in highly doped Bi{sub 1-x}Ca{sub x}MnO{sub 3}. Resonant x-ray diffraction was used at the Mn L-edge for the direct observation of the ordered localized states, and at the Mn K-edge for the sensitivity to the distortions of the manganese-oxygen octahedra. The orbital ordering on Mn atoms was directly observed at x=0.69; the analysis and the numerical simulations of the K-edge spectra allow us to characterize the pattern of the distorted octahedra at x = 4/5. These observations support the Wigner-crystal-type model at both dopings; the bi-stripe model is ruled out at x = 0.69.