The viational modes of matterMatteo BaggioliInstituto de Fisica TeoricaUAM-CISC, Madrid, Spain

Abstract: In the first part of the talk a theoretical description of the viational density of states (VDOS) of solids (both crystals and glasses) is presented starting from first principles. Without using any assumptions whatsoever about the existence and nature of 'disorder' in the material, it is shown analytically that the boson peak in the VDOS of both ordered crystals and glasses arises naturally from the competition between elastic mode propagation and viscous damping. The theory explains the recent experimental observations of boson peak in perfectly ordered crystals which cannot be explained based on previous theoretical frameworks. The theory also explains, for the first time, how the viational spectrum changes with the atomic density of the solid, and explains recent experimental observations of this effect.

In the second part, we will discuss the theoretical challenges introduced by the recent observation of low frequency solid-like elastic response in liquids. We will propose and motivate a possible resolution of the puzzle based on the so-called k-gap dispersion relation, providing a universal framework to understand the viational modes in both solids and liquids.

Web page of the Instituto de Fisica Teorica IFT Madrid

Cette conférence est présentée par le RQMP Versant Nord du Département de physique de l'Université de Montréal et de Génie physique de la Polytechnique.