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 β 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 β 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.

广泛使用的液体和玻璃势能态势（PEL）示意图给出的印象是，预先确定了从谷点到另一点通过鞍点的路径。但是，实际上，该路径更加随机且不可预测，因为在鞍点处消除了热历史，并且随机选择了向下的路径。在这里，我们通过对金属玻璃的结构激发进行原子模拟，通过研究β弛豫过程中的局部结构演变来解释这种令人困惑的行为。我们发现，PEL中的鞍态在短程顺序和原子动力学方面显示出普遍的熔体状特征，而与热历史和成分无关。我们认为，在鞍点处短暂的局部熔化是造成先前热史消失的原因。这解释了为什么β过程的活化和弛豫阶段解耦。这些发现凸显了理解鞍形状态在阐明系统动力学方面的重要性，并对当前关于PEL中系统演化的观点提出了疑问。