Compressed correlation functions and fast aging dynamics in metallic glasses

TL;DR

This study uses x-ray photon correlation spectroscopy to reveal that atomic dynamics in a metallic glass exhibit compressed, faster-than-exponential decay with universal aging behavior, indicating non-diffusive dynamics in the glassy state.

Contribution

It demonstrates the universality of compressed correlation functions and aging regimes in metallic glasses, providing a new understanding of their atomic dynamics below the glass transition.

Findings

Decay of density fluctuations is well described by compressed Kohlrausch-Williams-Watts functions.

Correlation functions can be rescaled to a single master curve.

Universal aging regimes persist deep in the glassy state.

Abstract

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