Spin-Orbital Entanglement and Violation of the Goodenough-Kanamori Rules

TL;DR

This paper demonstrates that quantum entanglement of spin and orbital degrees of freedom in certain Mott insulators causes dynamic interactions and apparent violations of traditional superexchange rules, revealing complex quantum behavior.

Contribution

It reveals the role of spin-orbital entanglement in causing fluctuations and violations of the Goodenough-Kanamori rules in $t_{2g}$ orbital systems.

Findings

Large spin-orbital fluctuations due to entanglement

Dynamical superexchange interactions fluctuate in sign

Violation of classical superexchange rules observed

Abstract

We point out that large composite spin-orbital fluctuations in Mott insulators with $t_{2g}$ orbital degeneracy are a manifestation of quantum entanglement of spin and orbital variables. This results in a dynamical nature of the spin superexchange interactions, which fluctuate over positive and negative values, and leads to an apparent violation of the Goodenough-Kanamori rules. [{\it Published in Phys. Rev. Lett. {\bf 96}, 147205 (2006).}]