Phonon Anomalies in La ₂ NiO ₄

Abstract

The phonon dispersion curves of La2NiO4 which is isostructural to La2CuO4 have been investigated by inelastic neutron scattering. Pronounced anomalies have been found in those phonon branches which involve the in-plane oxygen-nickel stretching vibrations. In particular, the breathing-type modes are strongly renormalized, in good accordance with recent theories of electron-phonon coupling in these compounds.