Polaronic orbital polarization in a layered colossal magnetoresistive manganite

The striking anisotropy observed in Huang scattering distributions near the intense Bragg reflections of La1.2Sr1.8Mn₂O₇ is shown to be the result of orbitally polarized polarons in the paramagnetic insulating state above TC. X-ray single-crystal diffuse scattering patterns from this bilayered colossal magnetoresistive manganite are calculated in terms of the polaronic local structure and compared with experimental measurements. At 300 K, the polaronic eg electrons occupy ``out-of-plane'' (i.e., 3z²-r²) orbitals, leading to MnO₆ octahedra that are Jahn-Teller elongated along the c axis, perpendicular to the perovskite layers. Between 300 K and TC, however, the ``orbital polarization'' is shown to shift into the a-b plane (i.e., 3x²-r² and 3y²-r² orbitals), allowing the formation of nanoscale polaron correlations above TC.