Wave vector dependence of the dynamics in supercooled metallic liquids.

We present a detailed investigation of the wave vector dependence of collective atomic motion in Au49Cu26.9Si16.3Ag5.5Pd2.3 and Pd42.5Cu27Ni9.5P21 supercooled liquids close to the glass transition temperature. Using x-ray photon correlation spectroscopy in a precedent uncovered spatial range of only few interatomic distances, we show that the microscopic structural relaxation process follows in phase the structure with a marked slows down at the main average inter-particle distance. This behavior is accompanied by dramatic changes in the shape of the intensity correlation functions which suggest the presence of large dynamical heterogeneities at length-scales corresponding to few icosahedral clusters. Distinct mechanisms of particle motion appear to govern the structural relaxation of the two systems in the highly viscous phase, which result in a Q-independent dynamic for the Pd-based alloy, and a ballistic-like mechanism of transport in the highly viscous Au-based liquid.