Neutron Brillouin scattering and low-Q dynamics in condensed matter

Neutron Brillouin scattering (NBS) is an inelastic neutron scattering near the forward direction. This technique is effective for observing coherent excitations in non-single-crystal samples, such as ferromagnetic spin waves in powder samples and acoustic phonons in liquids and polycrystals. Such excitations can be observed by accessing the energy-momentum space around the zero momentum. Although the principle of NBS is not new, the recent progress of intense pulsed neutron sources provides opportunities to realize the experimental conditions for NBS more conveniently by utilizing neutrons with higher energies and higher resolutions. The aim of this review article is to provide a brief description of the state-of-the-art inelastic neutron spectrometer, High Resolution Chopper Spectrometer (HRC), installed at J-PARC (Japan Proton Accelerator Research Complex), as well as the most recent results produced by HRC. The aim of NBS is to become a promising experimental method combined with intense pulsed neutrons for a wide range of scientific studies. (author)