Orbital Ordering inLa0.5Sr1.5MnO4Studied by Soft X-Ray Linear Dichroism

Abstract

We found that the conventional model of orbital-ordering of $3x^2-r^2/3y^2-r^2$ type in the $e_g$ states of ${\mathrm{L}\mathrm{a}}_{0.5}{\mathrm{S}\mathrm{r}}_{1.5}{\mathrm{M}\mathrm{n}\mathrm{O}}_4$ is incompatible with measurements of linear dichroism in the Mn $2p$-edge x-ray absorption, whereas these $e_g$ states exhibit predominantly cross-type orbital ordering of $x^2-z^2/y^2-z^2$. $\mathrm{L}\mathrm{D}\mathrm{A}+\mathrm{U}$ band-structure calculations reveal that such a cross-type orbital-ordering results from a combined effect of antiferromagnetic structure, Jahn-Teller distortion, and on-site Coulomb interactions.