title: Probing a nonequilibrium einstein relation in an aging colloidal glass.
abstract: We present a direct experimental measurement of an effective temperature in a colloidal glass of laponite, using a micrometric bead as a thermometer. The nonequilibrium fluctuation-dissipation relation, in the particular form of a modified Einstein relation, is investigated with diffusion and mobility measurements of the bead embedded in the glass. We observe an unusual nonmonotonic behavior of the effective temperature: starting from the bath temperature, it is found to increase up to a maximum value, and then decrease back, as the system ages. We show that the observed deviation from the Einstein relation is related to the relaxation times previously measured in dynamic light scattering experiments.
authors.affiliation: Laboratoire de Biorhéologie et Hydrodynamique Physico-chimique UMR CNRS 7057 and Fédération de Recherche Matières et Systèmes Complexes FR 2438, 2 Place Jussieu, Case 7056, 75251 Paris Cedex 05, France.
authors.forename: Bérengère
authors.initials: B
authors.lastname: Abou
authors.forename: François
authors.initials: F
authors.lastname: Gallet