Elementary excitations of magnetically ordered systems with orbital degeneracy

TL;DR

This paper develops a quantum flavor wave theory for magnetically ordered systems with orbital degeneracy, revealing coupled spin, orbital, and spin-orbital excitations with unique dispersion properties.

Contribution

It generalizes the Holstein-Primakoff transformation to include orbital degrees of freedom, introducing a new framework for analyzing elementary excitations in such systems.

Findings

Coupled spin and spin-orbital waves due to orbital anisotropy and Hund's rule.

Observation of new modes via inelastic neutron scattering.

In the SU(4) limit, flavor waves are dispersionless along certain directions.

Abstract

The Holstein-Primakoff transformation is generalized to develop a quantum flavor wave theory for spin systems with orbital degeneracy. Elementary excitations consist of spin, orbital, and spin-orbital waves. Spin and spin-orbital waves couple each other due to orbital anisotropy and Hund's rule, resulting in new modes observable by inelastic neutron scattering. In the SU(4) limit, flavor waves are dispersionless along one or more directions, and give rise to quantum fluctuations of reduced dimensionality.