Lattice Distortion and Resonant X-Ray Scattering in DyB_2C_2 (Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties)

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We study the resonant x-ray scattering (RXS) spectra at the Dy L_<III> absorption edge in the quadrupole ordering phase of DyB_2C_2. Analyzing the buckling of sheets of B and C atoms, we construct an effective model that the crystal field is acting on the 5d and 4f states with the principal axes different for different sublattices. Treating the 5d states as a band and the 4f states as localized states, we calculate the spectra within the dipole transition. We take account of processes that (1) the lattice distortion directly modulates the 5d states and (2) the charge anisotropy of the quadrupole ordering 4f states modulates the 5d states through the 5d-4f Coulomb interaction. Both processes give rise to the RXS intensities on (00 l/2) and (h0 l/2) spots. Both give similar photon-energy dependences and the same azimuthal-angle dependences for the main peak, in agreement with the experiment. The first process is found to give the intensities much larger than the second one in a wide parameter range of crystal field. This suggests that the main- peak of the RXS spectra is not a direct reflection of the quadrupole order but mainly controlled by the lattice distortion.
社団法人日本物理学会の論文
2003-05-15