“Non-simple liquids”—a challenge for neutron Brillouin scattering?

Neutron Brillouin scattering (NBS), i.e. inelastic neutron scattering (INS) at low scattering angles, is one of the best suited experimental techniques to study the collective atomic dynamics of liquids. With new NBS instrumentation (e.g. the BRISP spectrometer) and complementary development of inelastic X-ray scattering (IXS) spectrometers, new perspectives are currently being opened up for the extension of dynamical studies from simple to more complex liquids. In a series of INS experiments, the dependence of the atomic dynamics on the dominant type of atomic interaction was studied for binary Zintl-type liquids. The dispersion curves of collective modes show interesting deviations from the behaviour known from simple liquids, e.g. the splitting of the dispersion in liquid Na_xSn_1−x alloys around the position of the principal peak of S(Q). To understand the evolution of the dynamic modes and the corresponding relaxation processes over an extended range of momentum transfers, Q, combined neutron and X-ray Brillouin scattering experiments will be necessary followed by advanced theoretical modelling.