Disorder-induced mixing of transverse and longitudinal polarizations and Rayleigh anomalies: theory and experimental verification

Maria Grazia Izzo, Bjorn Wehinger, Giancarlo Ruocco, Aleksandar Matic, Claudio Masciovecchio, Alessandro Gessini, Stefano Cazzato

Published 2017-05-29Version 1

The propagation of acoustic waves through disordered media results in anomalous features in respect to Debye's theory. This is observed in attenuation, retardation and depolarization of real systems, as predicted by the elementary elasticity theory and experimentally observed in real systems. Each of these phenomena have attracted a large interest when dealing with topologically disordered media but, even if originating from the same root, they have been treated separately. Stochastic description of topologically disordered media arises from the need to describe the effect of heterogeneous and undetermined structure of most real wave-transmitting media. Using a stochastic approach at wavelengths of the order of the characteristic length-scale of heterogeneities, allowed us to achieve a quantitative, experimentally corroborated and unified description of acoustic waves properties in a disordered medium. These include the low-frequency acoustic waves anomalies in the so-called Rayleigh region and the mixing of longitudinal and transverse polarizations occurring at higher wavevectors. Model predictions are compared to acoustic waves features and the vibrational density of states measured in an ionic glass. The excellent agreement obtained between theory and experiments reveals how a coherent description of elastic waves behavior in a disordered medium can be achieved.