Understanding the insulating phase in CMR manganites: Shortening of the Jahn-Teller long-bond across the phase diagram of La_{1-x} Ca_x Mn O_3

TL;DR

This study investigates how local Jahn-Teller distortions in La_{1-x} Ca_x Mn O_3 evolve across the phase diagram, revealing a continuous decrease in distortion magnitude with increasing Ca, challenging simple polaron models.

Contribution

The paper provides detailed neutron diffraction data showing the continuous reduction of Jahn-Teller distortions in the insulating phase, offering new insights into the local structure of CMR manganites.

Findings

Jahn-Teller distortion persists in the insulating phase for all Ca levels.

The magnitude of the distortion decreases with increasing Ca content.

Results challenge the simple small-polaron model for the insulating state.

Abstract

The detailed evolution of the magnitude of the local Jahn-Teller (JT) distortion in La_{1-x} Ca_x Mn O_3 is obtained across the phase diagram for 0 < x < 0.5 from high quality neutron diffraction data using the atomic pair distribution function (PDF) method. A local JT distortion is observed in the insulating phase for all Ca concentrations studied. However, in contrast with earlier local structure studies its magnitude is not constant, but decreases continuously with increasing Ca content. This observation is at odds with a simple small-polaron picture for the insulating state.