Light-scattering study of β-relaxation in CaKNO₃ and salol near the liquid-glass transition: idealized and extended mode coupling theory analysis

Depolarized light-scattering measurements have revealed the dynamics of CaKNO₃ and salol near their liquid-glass transition temperatures in the frequency range of ∼ 0.2 GHz to ∼ 4 THz. The two-step relaxation process predicted by the mode coupling theory was observed in the supercooled liquid near T_c. Idealized mode coupling theory analysis for the β-relaxation region provided reasonable agreement with the scaling predictions. The crossover temperature was identified from both above and below T_c. However, systematic differences between the experimental data and the idealized theoretical β-spectra were observed at low frequencies for temperatures near and below T_c. An extended mode coupling theory analysis, which includes the phonon-assisted hopping transport, provided a good description of the complete experimental β-spectra. The hopping rate was quantitatively estimated from the analysis. Transition regions and trajectories were found in the temperature-hopping rate plane.