title: Emergence of crystal-like atomic dynamics in glasses at the nanometer scale.
abstract: The vibrational dynamics of a permanently densified silica glass is compared to the one of an α-quartz polycrystal, the silica polymorph of the same density and local structure. The combined use of inelastic x-ray scattering experiments and ab initio numerical calculations provides compelling evidence of a transition, in the glass, from the isotropic elastic response at long wavelengths to a microscopic regime as the wavelength decreases below a characteristic length ξ of a few nanometers, corresponding to about 20 interatomic distances. In the microscopic regime the glass vibrations closely resemble those of the polycrystal, with excitations related to the acoustic and optic modes of the crystal. A coherent description of the experimental results is obtained assuming that the elastic modulus of the glass presents spatial heterogeneities of an average size a ~ ξ/2 π.
authors.affiliation: CNR-IMEM Institute, Parma Science Park, I-43124 Parma, Italy. giacomo.baldi@cnr.it
authors.forename: G
authors.initials: G
authors.lastname: Baldi
authors.forename: M
authors.initials: M
authors.lastname: Zanatta
authors.forename: E
authors.initials: E
authors.lastname: Gilioli
authors.forename: V
authors.initials: V
authors.lastname: Milman
authors.forename: K
authors.initials: K
authors.lastname: Refson
authors.forename: B
authors.initials: B
authors.lastname: Wehinger
authors.forename: B
authors.initials: B
authors.lastname: Winkler
authors.forename: A
authors.initials: A
authors.lastname: Fontana
authors.forename: G
authors.initials: G
authors.lastname: Monaco