Dispersion of orbital excitations in 2D quantum antiferromagnets
  We map the problem of the orbital excitation (orbiton) in a 2D antiferromagnetic and ferroorbital ground state onto a problem of a hole in 2D antiferromagnet. The orbiton turns out to be coupled to magnons and can only be mobile on a strongly renormalized scale by dressing with magnetic excitations. We show that this leads to a dispersion relation reflecting the two-site unit cell of the antiferromagnetic background, in contrast to the predictions based on a mean-field approximation and linear orbital-wave theory. 
Krzysztof Wohlfeld, Maria Daghofer, Giniyat Khaliullin, Jeroen van den   Brink
cond-mat.str-el