title: Heterogeneous Viscoelasticity: A Combined Theory of Dynamic and Elastic Heterogeneity.
abstract: We present a heterogeneous version of Maxwell's theory of viscoelasticity based on the assumption of spatially fluctuating local viscoelastic coefficients. The model is solved in coherent-potential approximation. The theory predicts an Arrhenius-type temperature dependence of the viscosity in the vanishing-frequency limit, independent of the distribution of the activation energies. It is shown that this activation energy is generally different from that of a diffusing particle with the same barrier-height distribution, which explains the violation of the Stokes-Einstein relation observed frequently in glasses. At finite but low frequencies, the theory describes low-temperature asymmetric alpha relaxation. As examples, we report the good agreement obtained for selected inorganic, metallic, and organic glasses. At high frequencies, the theory reduces to heterogeneous elasticity theory, which explains the occurrence of the boson peak and related vibrational anomalies.
authors.affiliation: Dipartimento di Fisica, Universitá di Roma "La Sapienza", P'le Aldo Moro 2, I-00185 Roma, Italy.|Institut für Physik, Universität Mainz, Staudinger Weg 7, D-55099 Mainz, Germany.|Institut für Theoretische Physik, Leopold-Franzens-Universität Innsbruck, Technikerstraße 25/2, A-6020 Innsbruck, Austria.
authors.forename: Walter
authors.initials: W
authors.lastname: Schirmacher
authors.affiliation: Dipartimento di Fisica, Universitá di Roma "La Sapienza", P'le Aldo Moro 2, I-00185 Roma, Italy.|Center for Life Nano Science@Sapienza, Istituto Italiano di Tecnologia, V. Regina Elena 291, I-00161 Roma, Italy.
authors.forename: Giancarlo
authors.initials: G
authors.lastname: Ruocco
authors.affiliation: Dipartimento di Fisica, Universitá di Roma "La Sapienza", P'le Aldo Moro 2, I-00185 Roma, Italy.
authors.forename: Valerio
authors.initials: V
authors.lastname: Mazzone