热载流子冷却在光激发结构转变中的关键作用
The critical role of hot carrier cooling in optically excited structural transitions
摘要：
热载流子冷却发生在大多数的光激发诱导相变（PIPTs），但它的作用往往被忽视，在许多理论模拟以及在提出的机制。在这里，通过包括以前忽略的热载流子冷却的实时时间相关的密度泛函理论（rt-TDDFT）模拟，我们研究了热载流子冷却在PIPTs中的作用。以IrTe 2为例，我们揭示了超热电子从空间扩展态的高能级冷却到局域Ir-Ir二聚体反键态的低能级，显著增强了原子的驱动力，提高了原子的动能.这两个因素相结合，以溶解的Ir-Ir二聚体的原子运动的极限附近的时间尺度上，从而启动一个确定性的动力学相变。我们进一步证明，随后的冷却诱导光激发的电子和空穴的非辐射复合，导致实验观察到的Ir-Ir二聚体的超快恢复。这些发现提供了光激发结构相变中原子动力学的完整图像。
英文摘要：
The hot carrier cooling occurs in most photoexcitation-induced phase transitions (PIPTs), but its role has often been neglected in many theoretical simulations as well as in proposed mechanisms. Here, by including the previously ignored hot carrier cooling in real-time time-dependent density functional theory (rt-TDDFT) simulations, we investigated the role of hot carrier cooling in PIPTs. Taking IrTe2 as an example, we reveal that the cooling of hot electrons from the higher energy levels of spatially extended states to the lower energy levels of the localized Ir-Ir dimer antibonding states strengthens remarkably the atomic driving forces and enhances atomic kinetic energy. These two factors combine to dissolute the Ir-Ir dimers on a timescale near the limit of atomic motions, thus initiating a deterministic kinetic phase transition. We further demonstrate that the subsequent cooling induces nonradiative recombination of photoexcited electrons and holes, leading to the ultrafast recovery of the Ir-Ir dimers observed experimentally. These findings provide a complete picture of the atomic dynamics in optically excited structural phase transitions.
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