Fractionalization of Electron's Spin and Orbital Degrees of Freedom in Quasi-1D Cuprate
In contrast to magnetic excitations, the dispersive orbital excitations (orbitons) are generally considered to be very hard to detect. While this situation has improved tremendously with the "arrival" of the high resolution resonant inelastic x-ray scattering (RIXS), it was only very recently that RIXS unambiguously detected an orbiton.
In this talk I will explain the deep theoretical reasons for this situation: It occurs that in compounds with antiferromagnetic ground states there is an inherent coupling between orbital excitations and spin fluctuations which leads to the failure of the independent orbiton picture. While this coupling largely suppresses orbiton motion in 2D and 3D and explains the lack of orbiton dispersion seen by RIXS in many transition metal oxides, in 1D the electron's spin and orbital degree of freedom separate allowing for large orbiton dispersion as detected in the above mentioned recent RIXS experiment on quasi-1D cuprate. The general message is: not only spin and charge degrees of freedom can fractionalize in 1D but also the spin and orbital degrees of freedom can do it.