Unified picture of structural relaxation, beta relaxation, and excess wing in glass formers

We study the microscopic origins of relaxation modes revealed by spectroscopic studies of glasses. Major features in calorimetric and structural relaxation spectra, including α peaks, β peaks, and excess wings, are reproduced using a distinguishable-particle lattice model. It is based on void-induced particle hops, which model stringlike particle hopping motions. Excess wings are found to be flattened variants of β peaks when particle hopping barriers admit a wide distribution. A β relaxation event is attributed to the hop of a particle which neighbors a void. An α relaxation event involves a similar process by an arbitrary particle but also includes, as a prior step, the arrival of a diffusing void to become its neighbor.