The Study of Orbital Ordering with Resonant X-ray Scattering.

The article introduces the resonant X-ray scattering (RXS) as a technique to detect the orbital ordering of electrons. Magnetic ions in a highly symmetrical crystalline field may have an orbital degeneracy in the ground state. When the electrons partially occupy the degenerate states, it is defined as a system having orbital degrees of freedom. Further, the RXS can be applied to the detection of the orbital ordering in f-electron systems, that is, quadrupolar ordering. The much weaker coupling between the orbital degree of freedom and the lattice in 4f-electron systems makes them an ideal platform to study orbital interactions originating from electronic mechanisms.