Mechanism of resonant X-ray scattering in DyB2C2

For elucidating the relation between the resonant X-ray scattering (RXS) signal and the orbital order, we calculate the RXS spectra near the Dy LIII absorption edge in DyB2C2, in the antiferro-quadrupole (AFQ) ordering phase. Using a microscopic model that the 4f states of Dy are atomic while the 5d states form an energy band with a reasonable density of states, we obtain sufficient RXS intensities on the AFQ superlattice spots assuming the quadrupole order in the 4f states but without any lattice distortion, in good agreement with the recent experiment. The present result demonstrates the mechanism that the intensity is brought about by the modulation of 5d states through the anisotropic term of the 5d-4f Coulomb interaction