Fractionalization of electron's spin and orbital degrees of freedom in 1D

We show that electron's spin and orbital degrees of freedom can fractionalize in 1D antiferromagnets: although the orbital excitations are inherently coupled to spinons in antiferromagnetic Mott insulators, in 1D they separate into a {\it pure} orbiton and a single spinon. This is similar to the spin-charge separation in 1D but corresponds to an exotic regime where spinons are faster than holons [1]. The resulting large dispersion of the pure orbiton can be detected in e.g. quasi-1D cuprates [2]. [1] K. Wohlfeld, M. Daghofer, S. Nishimoto, G. Khaliullin, and J. van den Brink, Phys. Rev. Lett. {\bf 107}, 147201 (2011). [2] J. Schlappa {\it et al.}, to be published (2011).