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-forming materials at temperatures ranging from above the melting temperature T_m to below the calorimetric glass transition temperature T_g in the frequency range 0.2 GHz to 4000 GHz. The experimental susceptibility spectra χ(ω) exhibit both the form and the scaling properties predicted by the idealized mode coupling theory. In particular, the scaling frequency ω_σ was found to obey the power law ω_σ ∞{divides}T - T_C{divides}^2a for three different materials, 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, including activated transport.