Nature of Orbital Ordering in La_0.5Sr_1.5MnO_4 is Studied by Soft X-ray Linear Dichroism

TL;DR

This study reveals that the orbital ordering in La_0.5Sr_1.5MnO_4 is of a cross-type, contrary to conventional models, due to complex interactions including magnetic structure, lattice distortion, and electron correlations.

Contribution

The paper demonstrates that the orbital ordering in La_0.5Sr_1.5MnO_4 is of a cross-type, supported by experimental linear dichroism and LDA+U calculations, challenging previous models.

Findings

Conventional 3x^2-r^2/3y^2-r^2 orbital model is incompatible with measurements.

Cross-type x^2-z^2/y^2-z^2 orbital ordering is observed.

Orbital ordering results from combined effects of magnetic, Jahn-Teller, and Coulomb interactions.

Abstract

We found that the conventional model of orbital ordering of 3x^2-r^2/3y^2-r^2 type in the eg states of La_0.5Sr_1.5MnO_4 is incompatible with measurements of linear dichroism in the Mn 2p-edge x-ray absorption, whereas these eg states exhibit predominantly cross-type orbital ordering of x^2-z^2/y^2-z^2. LDA+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.