Understanding the Low-Frequency Quasilocalized Modes in Disordered Colloidal Systems

In disordered colloidal systems, we experimentally measure the normal modes with the covariance matrix method and clarify the origin of low-frequency quasilocalization at the single-particle level. We observe important features from both jamming and glass simulations: There is a plateau in the density of
states [D(w)] which is suppressed upon compression, as predicted by jamming; within the same systems,
we also find that the low-frequency quasilocalization originates from the large vibrations of defective
structures coupled with transverse excitations, consistent with a recent glass simulation. The coexistence
of these features demonstrates an experimental link between jamming and glass. Extensive simulations
further show that such a structural origin of quasilocalization is universally valid for various temperatures
and volume fractions.