The striking anisotropy observed in Huang scattering distributions near the intense Bragg reflections of ${\mathrm{La}}_{1.2}{\mathrm{Sr}}_{1.8}{\mathrm{Mn}}_2{\mathrm{O}}_7$ is shown to be the result of orbitally polarized polarons in the paramagnetic insulating state above $T_C.$ 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 $e_g$ electrons occupy “out-of-plane” (i.e., ${3z}^2-r^2)$ orbitals, leading to ${\mathrm{MnO}}_6$ octahedra that are Jahn-Teller elongated along the c axis, perpendicular to the perovskite layers. Between 300 K and $T_C,$ however, the “orbital polarization” is shown to shift into the $\mathit{a}-\mathit{b}$ plane (i.e., ${3x}^2-r^2$ and ${3y}^2-r^2$ orbitals), allowing the formation of nanoscale polaron correlations above $T_C.$

• Received 30 August 2002

DOI:https://doi.org/10.1103/PhysRevB.67.020409