Intrinsic coupling of orbital excitations to spin fluctuations in Mott insulators

TL;DR

This paper explores how the intrinsic coupling between orbital and spin degrees of freedom in Mott insulators affects elementary excitations, revealing coupled modes and spin-orbital separation phenomena.

Contribution

It demonstrates the inherent coupling of orbitons with spin fluctuations and identifies conditions for spin-orbital separation in one-dimensional systems.

Findings

Orbitons become coupled with spin fluctuations in certain models.

Composite orbiton-magnon modes can fractionalize in one dimension.

Spin-orbital separation occurs when spinons are faster than orbitons.

Abstract

We show how the general and basic asymmetry between two fundamental degrees of freedom present in strongly correlated oxides, spin and orbital, has very profound repercussions on the elementary spin and orbital excitations. Whereas the magnons remain largely unaffected, orbitons become inherently coupled with spin fluctuations in spin-orbital models with antiferromagnetic and ferroorbital ordered ground states. The composite orbiton-magnon modes that emerge fractionalize again in one dimension, giving rise to spin-orbital separation in the peculiar regime where spinons are faster than orbitons.