title: Boson peak and Ioffe-Regel criterion in amorphous siliconlike materials: The effect of bond directionality.
abstract: The vibrational properties of model amorphous materials are studied by combining complete analysis of the vibration modes, dynamical structure factor, and energy diffusivity with exact diagonalization of the dynamical matrix and the kernel polynomial method, which allows a study of very large system sizes. Different materials are studied that differ only by the bending rigidity of the interactions in a Stillinger-Weber modelization used to describe amorphous silicon. The local bending rigidity can thus be used as a control parameter, to tune the sound velocity together with local bonds directionality. It is shown that for all the systems studied, the upper limit of the Boson peak corresponds to the Ioffe-Regel criterion for transverse waves, as well as to a minimum of the diffusivity. The Boson peak is followed by a diffusivity's increase supported by longitudinal phonons. The Ioffe-Regel criterion for transverse waves corresponds to a common characteristic mean-free path of 5-7 Å (which is slightly bigger for longitudinal phonons), while the fine structure of the vibrational density of states is shown to be sensitive to the local bending rigidity.
authors.affiliation: Ioffe Physical Technical Institute, 194021 St Petersburg, Russian Federation and Université Montpellier II, CNRS, Montpellier 34095, France.
authors.forename: Y M
authors.initials: YM
authors.lastname: Beltukov
authors.affiliation: Université de Lyon, MATEIS, INSA-Lyon, CNRS UMR5510, F-69621, France and Institut Lumière Matière, UMR 5306 Université Lyon 1-CNRS, F-69622 Villeurbanne Cedex, France.
authors.forename: C
authors.initials: C
authors.lastname: Fusco
authors.affiliation: Saint Petersburg State Polytechnical University, 195251 Saint Petersburg, Russian Federation.
authors.forename: D A
authors.initials: DA
authors.lastname: Parshin
authors.affiliation: Université de Lyon, LaMCoS, INSA-Lyon, CNRS UMR5259, F-69621, France and Institut Lumière Matière, UMR 5306 Université Lyon 1-CNRS, F-69622 Villeurbanne Cedex, France.
authors.forename: A
authors.initials: A
authors.lastname: Tanguy