Compressed correlation functions and fast aging dynamics in metallic glasses

摘要

We present x-ray photon correlation spectroscopy measurements of the atomicdynamics in a Zr67Ni33 metallic glass, well below its glass transitiontemperature. We find that the decay of the density fluctuations can be welldescribed by compressed, thus faster than exponential, correlation functionswhich can be modeled by the well-known Kohlrausch-Williams-Watts function witha shape exponent {\beta} larger than one. This parameter is furthermore foundto be independent of both waiting time and wave-vector, leading to thepossibility to rescale all the correlation functions to a single master curve.The dynamics in the glassy state is additionally characterized by differentaging regimes which persist in the deep glassy state. These features seem to beuniversal in metallic glasses and suggest a non diffusive nature of thedynamics. This universality is supported by the possibility of describing thefast increase of the structural relaxation time with waiting time using aunique model function, independently of the microscopic details of the system.