Local Structural Distortions Inducing Resonant Forbidden Reflections in LaMnO3

We have performed a complete resonant x-ray scattering (RXS) study at the Mn Kedge of LaMnO3. (h 0 0), (0 k 0) and (0 0 l) reflections with h, k and l=odd, were measured between 10 and 300 K. We observed strong resonant peaks at the three types of reflections. They exhibit dipolar character with a change of the light polarization plane from σ to π. The azimuth angular dependence of all these reflections showed a characteristic sine evolution of π-period. The energy dependence of the scattered intensity for (h 0 0) and (0 k 0) reflections was identical while different structures were observed for the (0 0 l) reflections. We did not observe any change either on the resonance intensity or on the shape when crossing the Néel temperature TN∼ 140 K. All resonances seem to be decoupled from the magnetic ordering and this is true even for (0 0 l) reflections, which correspond to the magnetic ordering direction. The tensor analysis indicates that the azimuth behavior of these reflections is reproduced by considering the crystallographic octahedral tilts.