Dynamics of supercooled liquids: excess wings,β peaks, and rotation–translation coupling

Abstract

Dielectric susceptibility spectra of liquids cooled towards the liquid–glasstransition often exhibit secondary structure in the frequency region between theα peak andthe susceptibility minimum, in the form of either an ‘excess wing’ or a secondary peak—the Johari–Goldsteinβ peak. Recently, Götze and Sperl (2004 Phys. Rev. Lett. 92 105701) showed that a simpleschematic mode coupling theory model, which incorporates rotation–translation(RT) coupling, successfully describes the nearly logarithmic decay observedin optical Kerr effect data. This model also exhibits both excess wing andβ peak features, qualitatively resembling experimental dielectric data. It also predicts thatthe excess wing slope decreases with decreasing temperature and gradually evolves into aβ peak with increasing RT coupling. We therefore suggest that these features andtheir observed evolution with temperature may be consequences of RT coupling.