Length-scale dependence of the anomalous atomic motion in metallic glasses

Kurzfassung

Establishing microscopic structure–dynamics relations in glasses is essential for developing a comprehensive theory yet remains challenging owing to limited access to the relevant time and length scales. Here we probe density fluctuations in three metallic glasses and describe a complex organization of the dynamics that provides a framework of the anomalous compressed relaxation universally observed in metallic glasses at the atomic level. We demonstrate that this faster-than-exponential motion occurs only at length scales characterized by medium-range order and originates from internal stresses stored during the freezing of rigid domains across the glass transition. At larger length scales, the dynamics becomes stationary and heterogeneous, with stretched exponential relaxations reflecting the statistically averaged motions of different domains. We also identify a second independent relaxation, associated with persistent liquid-like motions, whose strength increases at large wavelengths. These findings reveal the cooperative, multiscale nature of relaxations in glasses.