Quantum behavior of Orbitals in Ferromagnetic Titanates: Novel Orderings and Excitations

TL;DR

This paper explores the quantum properties of orbital angular momentum in ferromagnetic titanates, revealing multiple orbital orderings and predicting experimental signatures for neutron scattering to identify these states.

Contribution

It introduces the quantum selection of four distinct orbital orderings in a frustrated orbital system with specific experimental predictions.

Findings

Identification of four orbital orderings including quadrupolar and weak orbital magnetism.

Quantum effects lift classical degeneracy, selecting specific orbital states.

Predictions for neutron scattering experiments to detect orbital orderings and excitations.

Abstract

We investigate the collective behavior of orbital angular momentum in the spin ferromagnetic state of a Mott insulator with $t_{2g}$ orbital degeneracy. The frustrated nature of the interactions leads to an infinite degeneracy of classical states. Quantum effects select four distinct orbital orderings. Two of them have a quadrupolar order, while the other states show in addition weak orbital magnetism. Specific predictions are made for neutron scattering experiments which might help to identify the orbital order in YTiO$_3$ and to detect the elementary orbital excitations.