Orbital ordering in charge transfer insulators

TL;DR

This paper introduces a novel electronic mechanism for orbital ordering in charge transfer insulators, explaining experimental observations without relying on electron-lattice interactions and highlighting differences from Mott-Hubbard insulators.

Contribution

It proposes a new purely electronic mechanism for orbital ordering that can alter the ground state of charge transfer insulators, distinct from traditional exchange interactions.

Findings

Orbital ordering can occur independently of lattice effects in charge transfer insulators.

The mechanism explains higher orbital ordering temperatures compared to spin ordering.

Application to materials like K2CuF4 demonstrates the model's relevance.

Abstract

We discuss a new mechanism of orbital ordering, which in charge transfer insulators is more important than the usual exchange interactions and which can make the very type of the ground state of a charge transfer insulator, i.e. its orbital and magnetic ordering, different from that of a Mott-Hubbard insulator. This purely electronic mechanism allows us to explain why orbitals in Jahn-Teller materials typically order at higher temperatures than spins, and to understand the type of orbital ordering in a number of materials, e.g. K_2CuF_4, without invoking the electron-lattice interaction.