Dynamics of Multipoles and Neutron Scattering Spectra in Quadrupolar Ordering Phase of CeB₆

Excitations and neutron scattering spectra in the antiferro-quadrupolar ordering phase of CeB 6 are studied theoretically. We develop a general formulation of the boson expansion method of multipoles and clarify the selection rules governing the multipolar dynamics. We apply the method to the RKKY model, which was introduced before for this material, and discuss the dispersions of excitation energies and their dependence on the magnetic field. Then neutron scattering spectra are calculated within the dipole approximation and compared quantitatively with the experiments by Bouvet. Possible interpretations of the peak structures in the observed spectra are discussed in connection with the characteristic multipolar interactions in CeB 6 .