Universal nature of the saddle states of structural excitations in metallic glasses

A widely used schematic picture of the potential energy landscape (PEL) for liquid and glass gives an impression that the pathway of moving from a valley to another through a saddle point is predetermined. However, in reality the pathway is much more stochastic and unpredictable because thermal history is wiped out at the saddle point and the pathway down is randomly chosen. Here we explain this puzzling behavior through the study of local structural evolutions in the beta relaxation process by atomistic simulations of structural excitations for metallic glasses. We find that the saddle states in the PEL show universal melt-like features in short-range order and atomic dynamics, independent of thermal history and composition. We propose that the short-lived local melting at the saddle point is responsible for wiping out the prior thermal history. This explains why the activation and relaxation stages of the b process are decoupled. The findings highlight the importance of understanding the nature of the saddle states in elucidating the system dynamics, and pose a question on the current view on the system evolution in the PEL. (C) 2021 The Author(s). Published by Elsevier Ltd.

Automated summary

This study investigates the local structural evolutions in the beta relaxation process of metallic glasses through atomistic simulations, revealing universal melt-like features in the saddle states of the PEL. The short-lived local melting at the saddle point is found to wipe out prior thermal history, providing an explanation for the decoupling of activation and relaxation stages in the b process. These findings emphasize the importance of understanding the nature of saddle states in elucidating system dynamics and raise questions about the current view on system evolution in the PEL.