High-resolution study of the supposed fourfold Nd spin-wave degeneracy of Nd2CuO4

Model predictions for the Nd spin-wave dispersion in Nd2CuO4 have been test ed with high-resolution inelastic neutron scattering on a single crystal at T = 0.5 K. A Heisenberg model in the random phase approximation has been p reviously proposed which predicts two dispersionless fourfold degenerate mo des along the crystallographic AM direction. This particular feature is a c onsequence of the symmetry and of the type of interactions considered in th e Hamiltonian. Our data unambiguously reveal additional peaks along AM whic h were previously unresolved. Possible origins for the lifting of the fourf old degeneracy of the modes along the AM direction are discussed.