Soft X-ray investigation of strongly correlated electron systems

Soft X-ray spectroscopy plays an important role for understanding the electronic structure of correlated electron materials. We review two examples of soft X-ray spectroscopic investigation on electron correlations and orbital symmetry in transition-metal oxides. The measurements show the existence of Coulomb correlations in CrO2 and the Mott-Hubbard character of 3d electrons. We conclude that CrO2 has a dualistic electronic nature, in which the states at the Fermi level are bandlike and while those at higher energies are strongly localized of completely different origin and symmetry. In addition, we demonstrate that linear dichroism in Mn 2p X-ray absorption is a powerful method to test the validity of models for orbital ordering in transition-metal oxides. Our linear dichroism measurements indicate that orbital ordering of the Mn eg electrons in La0.5Sr1.5MnO4 is dominated by x2−z2/y2−z2 type of ordering.