Inelastic x-ray scattering (IXS) measurements of the dynamic structure factor in liquid Na57K43, sensitive to the atomic-scale coarse graining, reveal a sound velocity value exceeding the long wavelength, continuum value and indicate the coexistence of two phonon-like modes. Applying Generalized Collective Mode (GCM) analysis scheme, we show that the positive dispersion of the sound velocity occurs in a wavelength region below the crossover from hydrodynamic to atom-type excitations and, therefore, it can not be explained as sound propagation over the light specie (Na) network. The present result experimentally proves the existence of positive dispersion in a binary mixture due to a relaxation process, as opposed to fast sound phenomena.
@article{arxiv.0803.0493,
title = {Crossover between hydrodynamic and kinetic modes in binary liquid alloys},
author = {Stefano Cazzato and Tullio Scopigno and Taras Bryk and Ihor Mryglod and Giancarlo Ruocco},
journal= {arXiv preprint arXiv:0803.0493},
year = {2009}
}
Comments
7 pages, 8 figures, to appear in "Physical Review B"