Initial Atomic Motion Immediately Following Femtosecond-Laser Excitation in Phase-Change Materials
Initial Atomic Motion Immediately Following Femtosecond-Laser Excitation in Phase-Change Materials
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DOI：
10.1103/physrevlett.117.135501
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发表时间：
2016-09-21
影响因子：
8.6
通讯作者：
Yamada, N.
中科院分区：
文献类型：
--
作者：
Matsubara, E.;Okada, S.;Yamada, N.
尽管相变材料广泛用于数据存储，但对其超快相变及其伴随的大而快速的光学变化的独特机制尚未达成共识。通过采用飞秒光学激光和X射线自由电子激光相结合的泵浦探针观察方法，我们通过实验证实，在GeTe和Ge2Sb2Te5晶体中，在飞秒光学激光照射后，主要是Ge原子发生了保持偏心位置的颤动运动，最终导致更高的对称性或无序状态。未畸变晶格中的这种非常初始的嘎嘎声运动可能与由于 GeTe 基相变材料特征的共振键的损失而导致的瞬时光学变化有关。基于第一原理分子动力学模拟得出的非晶结构，我们推断出一种合理的通过非熔化的超快非晶化机制。
Despite the fact that phase-change materials are widely used for data storage, no consensus exists on the unique mechanism of their ultrafast phase change and its accompanied large and rapid optical change. By using the pump-probe observation method combining a femtosecond optical laser and an x-ray freeelectron laser, we substantiate experimentally that, in both GeTe and Ge2Sb2Te5 crystals, rattling motion of mainly Ge atoms takes place with keeping the off-center position just after femtosecond-optical-laser irradiation, which eventually leads to a higher symmetry or disordered state. This very initial rattling motion in the undistorted lattice can be related to instantaneous optical change due to the loss of resonant bonding that characterizes GeTe-based phase change materials. Based on the amorphous structure derived by first-principles molecular dynamics simulation, we infer a plausible ultrafast amorphization mechanism via nonmelting.