Observation of low energy excitations in μeV rang in Nd2CuO4

Complete text of publication follows. Neutron scattering experiments are presented on Nd2CuO4 at millikelvin temperatures by using a backscattering high resolution neutron spectrometer. The energy scans below 200 mK revealed inelastic peaks at about 1.5 μeV on both the energy gain and the energy loss side. The inelastic peaks moves gradually towards lower energy with increasing temperature and turns into a quasielatic-like peak at higher temperatures. The hyperfine induced nuclear polarization was reported of the Nd nuclear moments below about 200 mK evidenced by the anomalous increase of the intensity of the forbidden 1/2, 1/2, 0 superstructure reflection. We therefore expect nuclear spin wave excitations below about 200 mK because Nd nuclear moments are coupled through Shull-Nakamura indirect interaction. The observed inelastic peak at about 1.5 μeV can be interpreted to be due to the nuclear spin wave excitations. Alternatively the inelastic peak can be due to the neutron spin flip scattering caused by the nuclear transition between the hyperfine field split levels of Nd nuclei with spin I = 7/2. To our knowledge this is the first reported observation of the low energy excitations in Nd2CuO4 in μeV range. (author)