Sommaire:

A large class of materials, ranging from glasses to soft matter and biological systems, undergo structural arrest and physical aging. Following different experimental routes, like decreasing the temperature in a glass former liquid or increasing the packing fraction in a colloidal suspension, these materials can be driven in an out-of-equilibrium state, where their properties depend on the previous history of the system and spontaneously evolve with time. This process leads to an extremely complex dynamical scenario, characterized by a dramatic increase of the structural relaxation time and the emerging of multiple relaxation processes. The microscopic slow dynamics of out-of-equilibrium materials can be followed thanks to the unique properties of X-ray Photon Correlation Spectroscopy which probes the dynamics at the nanometric and atomic scale. Here I will present a detailed investigation of the relaxation processes occurring in metallic glasses during physical aging. Although the apparent differences, metallic glasses display an anomalous dynamics at the microscopic level which remembers that of complex soft materials, such as gels and concentrated colloidal suspensions. By combining dynamical and structural studies we have been able to quantitatively link for the first time this anomalous atomic motion to microscopic structural mechanisms usually observed in diffraction studies, providing a broader unique view of the glassy state.

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