Dynamic structure factor of non-crystalline and crystalline systems as revealed by MARI, a neutron chopper instrument

Abstract

Here we extracted information on the structure and dynamics of material from the momentum dependence of the dynamic structure factor S( Q, E), which is a function of momentum transfer Q and energy transfer E, and introduce a new concept called the dynamic pair correlation function (DPCF). We used the MARI (Multi-Angle Rotor Instrument) spectrometer, which uses neutron incident energies from 20 meV to 2 eV with high energy resolution ∼ 1% ( ΔE/ E i) combined with a pulsed neutron source. The wide range of continuous detector angle enables access to a wide region of momentum-energy ( Q- E) space in a single measurement. With this advanced instrument, we were able to apply our newly developed data reduction scheme involving S( Q, E). The results demonstrate for the first time that intermediate correlation for non-crystalline material and local structural instability in crystalline systems can be determined clearly by this scheme. These observations are quite important to understand the universal thermal properties of non-crystalline materials and the mechanism of the high-Tc superconductivity respectively. Hence, to demonstrate the capability of this method involving the MARI and the DPCF scheme, we looked at two typical cases, vitreous silica, SiO 2 (a non-crystalline material) and a high- T c superconductor, YBa 2Cu 3O 7, (a crystalline material).