Orbital order out of spin disorder: How to measure the orbital gap

TL;DR

This paper explores how orbital order and the orbital excitation gap in a Mott-Hubbard insulator arise from spin disorder, proposing a method to measure the gap via inelastic neutron scattering.

Contribution

It demonstrates that the orbital gap results from an order-from-disorder mechanism and suggests a practical measurement approach using existing neutron scattering techniques.

Findings

Orbital order and gap are generated by order-from-disorder.

The orbital gap can be detected indirectly through spin structure factor.

Proposes a measurement method using inelastic neutron scattering.

Abstract

The interplay between spin and orbital degrees of freedom in the Mott-Hubbard insulator is studied by considering an orbitally degenerate superexchange model. We argue that orbital order and the orbital excitation gap in this model are generated through the order-from-disorder mechanism known previously from frustrated spin models. We propose that the orbital gap should show up indirectly in the dynamical spin structure factor; it can therefore be measured using the conventional inelastic neutron scattering method.