A surprising relation between double exchange and Heisenberg model spectra: Application to half-doped manganites

TL;DR

This paper demonstrates that spectra from double exchange and Heisenberg models are analytically identical in half-doped manganites, complicating the identification of the correct physical model despite different underlying physics.

Contribution

It reveals the spectral equivalence of two different models for Zener polarons, challenging the ability to distinguish the correct physical description from spectral data alone.

Findings

Spectra from both models are analytically identical.

The model spectrum accurately matches ab initio calculations.

Wavefunction analysis does not decisively favor one model.

Abstract

The Zener polarons recently found in half-doped manganites are usually seen as mixed valence entities ruled by a double exchange Hamiltonian involving only correlated electrons of the metals. They can however be considered as ferrimagnetic local units if the holes are localized on the bridging oxygen atoms as implicitely suggested by recent mean-field it ab initio calculations. In the latter case, the physics is ruled by a Heisenberg Hamiltonian involving magnetic oxygen bridges. This paper shows that the spectra resulting from the resolution of both models are analytically identical. This single resulting model spectrum accurately reproduces the spectrum of Zener polarons in Pr0.6Ca0.4MnO3 manganite studied by means of explicitely correlated ab initio calculations. Since the physics supported by each model are different, the analysis of the exact Hamiltonian ground state wave function should a priori enables one to determine the most appropriate model. It will be shown that neither the spectrum nor the wavefunction analysis bring any decisive arguments to settle the question. Such undecidability would probably be encountered in experimental information.