Breakdown of the Debye approximation for the acoustic modes with nanometric wavelengths in glasses

• DOI: 10.1073/pnas.0808965106
• Publication Date: 2009-02-25T03:56:26Z
• Authors: Giulio Monaco; Valentina M. Gior...
• Keywords: Mesoscopic physics; Debye; Debye model

On the macroscopic scale, wavelengths of sound waves in glasses are large enough that details disordered microscopic structure usually irrelevant, and medium can be considered as a continuum. decreasing wavelength this approximation must course fail at one point. We show here takes place unexpectedly on mesoscopic scale characteristic range order glasses, where it still works well for corresponding crystalline phases. Specifically, we find acoustic excitations with nanometric clear signature being strongly scattered, indicating existence cross-over between well-defined modes larger ill-defined ones smaller wavelengths. This region is accompanied by softening velocity quantitatively accounts excess observed vibrational density states over Debye level energies few milli-electronvolts. These findings thus highlight contribution to well-known universal low-temperature anomalies found specific heat glasses.