Inelastic X-ray Scattering of Valence Fluctuating YbPd

Abstract

Inelastic X-ray scattering (IXS) of cubic YbPd is carried out at 300 K to examine lattice instabilities associated with the valence ordering. The IXS spectra in the longitudinal -X (-X(L)) direction show that the phonon energy decreases from the middle of the zone to the zone boundary, which indicates the presence of a lattice instability at the X(L) point. On the other hand, normal IXS spectra are observed in the -X(T) and -M directions, which implies absense of any instabilities at the X(T) and M points. Although our previous diffraction measurements suggested a superlattice structure of either a a 2a or 2a 2a a below T = 105 K, the IXS results indicate that the a a 2a structure is much more convincing. The broad linewidth of the IXS spectra observed at around the X(L) point is possibly due to strong electron-phonon coupling, not to the Q-resolution in the IXS measurements.