Orbital order in La0.5Sr1.5MnO4: beyond a common local Jahn-Teller picture

TL;DR

This study reveals that in layered manganites like La0.5Sr1.5MnO4, orbital ordering cannot be accurately determined solely from local Jahn-Teller distortions, highlighting the importance of long-range crystal field effects and anisotropic hopping.

Contribution

It demonstrates that standard local distortion assumptions are insufficient for layered systems and emphasizes the role of long-range effects in orbital ordering.

Findings

Orbital ordering contradicts local distortion predictions.

Long-range crystal field effects are crucial.

Anisotropic hopping influences orbital occupation.

Abstract

The standard way to find the orbital occupation of Jahn-Teller (JT) ions is to use structural data, with the assumption of a one-to-one correspondence between the orbital occupation and the associated JT distortion, e.g. in O6 octahedron. We show, however, that this approach in principle does not work for layered systems. Specifically, using the layered manganite La0.5Sr1.5MnO4 as an example, we found from our x-ray absorption measurements and theoretical calculations, that the type of orbital ordering strongly contradicts the standard local distortion approach for the Mn3+O6 octahedra, and that the generally ignored long-range crystal field effect and anisotropic hopping integrals are actually crucial to determine the orbital occupation. Our findings may open a pathway to control of the orbital state in multilayer systems and thus of their physical properties.