# Local structure study of the orbital order/disorder transition in LaMnO$_3$

## TL;DR

This study investigates the local structural changes in LaMnO₃ during its orbital order-disorder transition using neutron and X-ray PDF analysis, revealing a discontinuous transition and supporting an anisotropic Potts model.

## Contribution

It provides new insights into the local structural behavior across the transition, challenging conventional models and favoring the anisotropic Potts model for LaMnO₃.

## Key findings

- Discontinuous change in local structure at the transition.
- Local orbital arrangements in ordered regime match average structure.
- Preference for anisotropic Potts model in disordered regime.

## Abstract

We use a combination of neutron and X-ray total scattering measurements together with pair distribution function (PDF) analysis to characterise the variation in local structure across the orbital order--disorder transition in LaMnO$_3$. Our experimental data are inconsistent with a conventional order--disorder description of the transition, and reflect instead the existence of a discontinuous change in local structure between ordered and disordered states. Within the orbital-ordered regime, the neutron and X-ray PDFs are best described by a local structure model with the same local orbital arrangements as those observed in the average (long-range) crystal structure. We show that a variety of meaningfully-different local orbital arrangement models can give fits of comparable quality to the experimental PDFs collected within the disordered regime; nevertheless, our data show a subtle but consistent preference for the anisotropic Potts model proposed in \emph{Phys Rev.\ B} {\bf 79}, 174106 (2009). The key implications of this model are electronic and magnetic isotropy together with the loss of local inversion symmetry at the Mn site. We conclude with a critical assessment of the interpretation of PDF measurements when characterising local symmetry breaking in functional materials.