RESONANT X-RAY-SCATTERING FROM ORBITAL ORDERING IN LAMNO3

Dipole resonant x-ray scattering from ordered Mn 3d orbitals in LaMnO3 has been observed near the Mn K-absorption edge. The polarization of the scattered photons is rotated from sigma to pi' and the azimuthal a ngle dependence shows a characteristic twofold symmetry. A theory for the resonant scattering mechanism has been developed by considering th e splitting of the Mn 4p levels due to the Mn 3d orbital ordering. The order parameter of the orbital ordering decreases above the Neel temp erature (T-N = 140 K) and disappears at T-0 = 780 K, concomitant with a structural phase transition.