Liu Hao-Wen, Liu Wen-Hao, Suo Zhao-Jun, Wang Zhi, Luo Jun-Wei, Li Shu-Shen, Wang Lin-Wang
State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China.
Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China.
Proc Natl Acad Sci U S A. 2022 Jul 12;119(28):e2122534119. doi: 10.1073/pnas.2122534119. Epub 2022 Jul 6.
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 method, here we track the motion of individual vanadium (V) ions during PIPT in VO 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.
光致相变（PIPT）一直被视为一个相干过程，但最近的实验中观察到了PIPT中的超快无序现象。利用实时含时密度泛函理论方法，我们在此追踪了VO中PIPT过程中单个钒（V）离子的运动，并发现可以通过调节激光能量密度来操控其相干或无序动力学。我们发现，光激发空穴在每个V-V二聚体上产生一个力，以驱动它们的集体相干运动，这与热致振动相互竞争。如果激光能量密度非常低，以至于光激发空穴密度过低而无法单独驱动相变，那么由于热声子的干扰，PIPT就是一个无序过程。我们还揭示，如果激光能量密度过高，由V-V二聚键合态填充的光激发空穴会饱和，从而限制了光致相变的时间尺度。
