Coherent dynamic structure factor of orthoterphenyl around the mode coupling crossover temperatureTc

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