Orbital Ordering of Manganites Studied by Soft X-ray Linear Dichroism

Correlated-electron materials such as transition-metal oxides have attracted enormous interest because of their interesting physical properties, including superconductivity and colossal magnetoresistance. An electron in a correlated electron material has three attributes: charge, spin, and orbital. The orbital represents the shape of the electron distribution, and the orbital degree of freedom plays an important role in novel properties of correlatedelectron materials through strong coupling with charge, spin, and lattice dynamics. From measurements of linear dichroism in Mn 2p-edge x-ray absorption, we found that single-layered manganite La0.5Sr1.5MnO4 exhibits predominantly cross-type orbital ordering, in sharp contrast to the previous understanding of rod-type orbital ordering. Band-structure calculations also reveal that such a cross-type orbital ordering results from a combined effect of antiferromagnetic structure, Jahn-Teller distortion, and on-site Coulomb interactions.