Relaxation Decoupling in Metallic Glasses at Low Temperatures.

Upon cooling, glass-forming liquids experience a dynamic decoupling in the fast β and slow α process, which has greatly influenced glass physics. By exploring an extremely wide temporal and temperature range, we find a surprising gradual change of the relaxation profile from a single-step to a two-step decay upon cooling in various metallic glasses. This behavior implies a decoupling of the relaxation in two different processes in a glass state: a faster one likely related to the anomalous stress-dominated microscopic dynamics, and a slower one associated with subdiffusive motion at larger scales with a broader distribution of relaxation times.