光激发VO2中有序和无序动力学的统一
Uniting the order and disorder dynamics in photoexcited VO2
摘要：
光致相变（PIPT）一直被认为是一个相干过程，但在最近的实验中观察到了PIPT中的超快无序。利用实时含时密度泛函理论（rt-TDDFT）方法，我们跟踪了钒离子在VO 2中PIPT过程中的运动，发现它们的相干或无序动力学可以通过调节激光能量密度来控制。我们发现，光激发的空穴产生的每个V-V二聚体上的力，以驱动其集体相干运动，在竞争与热诱导振动。如果激光能量密度太低，光致空穴密度太低，不能单独驱动相变，则PIPT是由于热声子的干涉而引起的无序过程。我们还发现，如果激光能量密度太大，光致空穴中的V-V二聚成键态将趋于饱和，从而限制了光致相变的时间尺度。
英文摘要：
Photoinduced phase transition (PIPT) is always treated as a coherent process, but ultrafast disordering in PIPT is observed in recent experiments. Utilizing the real-time time-dependent density functional theory (rt-TDDFT) method, here, we track the motion of individual vanadium (V) ions during PIPT in VO2 and uncover that their coherent or disordered dynamics can be manipulated by tuning the laser fluence. We find that the photoexcited holes generate a force on each V-V dimer to drive their collective coherent motion, in competing with the thermal-induced vibrations. If the laser fluence is so weak that the photoexcited hole density is too low to drive the phase transition alone, the PIPT is a disordered process due to the interference of thermal phonons. We also reveal that the photoexcited holes populated by the V-V dimerized bonding states will become saturated if the laser fluence is too strong, limiting the timescale of photoinduced phase transition.
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