d-f Coulomb and quadrupole-strain interactions in DyB2C2 observed by resonant x-ray scattering

TL;DR

This study investigates the d-f Coulomb interaction in DyB2C2 using resonant x-ray scattering, revealing the opposite signs of quadrupolar moments of 4f and 5d electrons and their coupling with lattice distortions.

Contribution

It provides experimental evidence and analysis of the d-f Coulomb interaction and quadrupolar moments in DyB2C2 through resonant x-ray scattering techniques.

Findings

Quadrupolar moments of 4f and 5d electrons have opposite signs.

Interference between resonant and nonresonant scattering observed.

Direct coupling between 4f electrons and lattice confirmed.

Abstract

Experimental evidence of the d-f Coulomb interaction responsible for the resonant x-ray scattering (RXS) from antiferroquadrupolar order in DyB2C2 is presented. The energy dependences of the RXS intensity with polarization analysis are analyzed by considering the interference between the resonances of dipolar (E1) and quadrupolar (E2) transition processes. It is found that the structure factors for the E1 and E2 processes have the same sign for sigma-pi' but the opposite sign for sigma-sigma' channel. This result, when compared with the calculated structure factors, means that the quadrupolar moments of the 4f and 5d electrons have opposite signs to each other. Interference between nonresonant Thomson scattering from the lattice distortion and the resonant scatterings is also studied and a direct coupling between 4f and the lattice is concluded.