Orbital-order melting in rare-earth manganites: the role of super-exchange

TL;DR

This study investigates the mechanisms behind orbital-order melting in rare-earth manganites, revealing that super-exchange interactions are not the primary factor, and that crystal-field effects are more influential in the observed phenomena.

Contribution

The paper demonstrates that super-exchange interactions have a minor role in orbital-order melting, emphasizing the importance of crystal-field effects in rare-earth manganites.

Findings

Super-exchange yields a transition temperature T_KK that decreases with smaller rare-earth radius.

Pressure increases T_KK, contrary to experimental T_OO trends.

Crystal-field splitting further reduces T_KK, highlighting its significance.

Abstract

We study the mechanism of orbital-order melting observed at temperature T_OO in the series of rare-earth manganites. We find that many-body super-exchange yields a transition-temperature T_KK that decreases with decreasing rare-earth radius, and increases with pressure, opposite to the experimental T_OO. We show that the tetragonal crystal-field splitting reduces T_KK further increasing the discrepancies with experiments. This proves that super-exchange effects, although very efficient, in the light of the experimentally observed trends, play a minor role for the melting of orbital ordering in rare-earth manganites.