Spectroscopy of La<Subscript>0.5</Subscript>Sr<Subscript>1.5</Subscript>MnO<Subscript>4</Subscript> orbital ordering: a cluster many-body calculation

Orbital ordering (OO) in La<Subscript>0.5</Subscript>Sr<Subscript>1.5</Subscript>MnO<Subscript>4</S ubscript> has been studied using soft X-ray resonant diffraction (SXRD) at the Mn L<Subscript>2,3</Subscript> edges in combination with many-body cluster calculations. The SXRD intensity is modelled in second quantization using a small planar cluster consisting of a central active Mn site with first-neighbour shells comprising O and Mn sites. The effective Hamiltonian includes Slater-Koster parameters and charge transfer and electron correlation energies obtained from previous measurements on manganites. The energy dependence of the SXRD OO peak is calculated using the Jahn-Teller distortions of the oxygen octahedra and in-plane spin correlations as adjustable parameters. These contributions are clearly distinguished above the Néel temperature with a good spectroscopic agreement. The results also suggest a significant charge separation between the Mn sites. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2006