Breakdown of the Stokes-Einstein relation above the melting temperature in a liquid phase-change material.

The dynamic properties of liquid phase-change materials (PCMs), such as viscosity η and the atomic self-diffusion coefficient , play an essential role in the ultrafast phase switching behavior of novel nonvolatile phase-change memory applications. To connect η to , the Stokes-Einstein relation (SER) is commonly assumed to be valid at high temperatures near or above the melting temperature and is often used for assessing liquid fragility (or crystal growth velocity) of technologically important PCMs. However, using quasi-elastic neutron scattering, we provide experimental evidence for a breakdown of the SER even at temperatures above in the high-atomic mobility state of a PCM, GeSbTe.

X-Ray Photon Correlation Spectroscopy Reveals Intermittent Aging Dynamics in a Metallic Glass.

We use coherent x rays to probe the aging dynamics of a metallic glass directly on the atomic level. Contrary to the common assumption of a steady slowing down of the dynamics usually observed in macroscopic studies, we show that the structural relaxation processes underlying aging in this metallic glass are intermittent and highly heterogeneous at the atomic scale. Moreover, physical aging is triggered by cooperative atomic rearrangements, driven by the relaxation of internal stresses.