COHERENT DYNAMIC STRUCTURE FACTOR OF ORTHOTERPHENYL AROUND THE MODE-COUPLING CROSSOVER TEMPERATURE T-C

The coherent dynamic structure factor of supercooled orthoterphenyl ha s been measured by time-of-flight neutron scattering. The data extend previous backscattering and spin-echo data towards shorter times. In t he beta relaxation regime the two-step decay of density correlations c an be described by the same master function as found before for self-c orrelations. We show that the mode-coupling crossover temperature T-c can be determined from beta relaxation data alone. The wave-number dep endence of the relaxation amplitude follows, to some extent, that of t he static structure factor.