Intrinsic coupling of orbital excitations to spin fluctuations in Mott   insulators
  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. 
Krzysztof Wohlfeld, Maria Daghofer, Satoshi Nishimoto, Giniyat   Khaliullin, Jeroen van den Brink
cond-mat.str-el