Theoretical study of orbital ordering/fluctuation and resonant X-ray scattering in manganites

A theory of resonant X-ray scattering in manganites with orbital degree of freedom is presented. The scattering cross section is represented by the correlation function of the pseudospin operator for orbital degree of freedom of Mn ions by utilizing the group theory. Orbital order parameter, orbital fluctuation and their critical exponents are studied like those of spin/charge degrees of freedom done in the neutron/electron scatterings.