LIGHT-SCATTERING SPECTROSCOPY OF THE LIQUID-GLASS TRANSITION - COMPARISON WITH IDEALIZED AND EXTENDED MODE-COUPLING THEORY

Light scattering experiments were performed on several fragile glass-f orming materials at temperatures ranging from above the melting temper ature T(m) to below the calorimetric glass transition temperature T(g) in the frequency range 0.2 GHz to 4000 GHz. The experimental suscepti bility spectra chi''(omega) exhibit both the form and the scaling prop erties predicted by the idealized mode coupling theory. In particular, the scaling frequency omega(sigma) was found to obey the power law om ega(sigma) is-proportional-to \T - T(C)\2alpha for three different mat erials, confirming the predicted ''critical slowing down'' as T --> T( C) from either above or below. At low frequencies and temperatures the spectra deviate from the predictions due to the neglect of ergodicity -restoring activated transport (hopping) processes. We have therefore reanalyzed the data using the extended version of the theory, includin g activated transport.