Neutron Scattering Studies of the Model Glass Former Ortho-terphenyl

The van der Waals liquid orthoterphenyl has long been used as a model system in the study of the glass transition. Motivated by mode-coupling theory, extensive experiments have been undertaken to monitor the onset of structural relaxation on microscopic time and length scales. Using in particular quasielastic neutron scattering, the decay of density and tagged-particle correlations has been measured as a function of temperature, pressure and wave number. A consistent picture is developped in which the mode-coupling singularity appears as a change of transport mechanism in the moderately viscous liquid, at temperatures far above the conventional (caloric) glass transition.