光生载流子掺杂引起的单斜晶系VO $_2$的瞬时带隙崩塌
Instantaneous band gap collapse in photoexcited monoclinic VO$_2$ due to photocarrier doping
摘要：
使用飞秒时间分辨光电子能谱学我们证明，光激发转换单斜VO $_2$准瞬间到金属。因此，我们排除了VO $_2$光致电子相变的80飞秒结构瓶颈。第一性原理多体微扰理论计算揭示了VO $_2$带隙对动态屏蔽库仑相互作用变化的高灵敏度，支持完全电子驱动的等结构绝缘体到金属的转变。因此，我们得出结论，超快能带结构重整化是由光激发的载流子从本地化的V 3d价态，强烈改变屏蔽\emph{before}显着的热载流子弛豫或离子运动发生。
英文摘要：
Using femtosecond time-resolved photoelectron spectroscopy we demonstrate that photoexcitation transforms monoclinic VO$_2$ quasi-instantaneously into a metal. Thereby, we exclude an 80 femtosecond structural bottleneck for the photoinduced electronic phase transition of VO$_2$. First-principles many-body perturbation theory calculations reveal a high sensitivity of the VO$_2$ bandgap to variations of the dynamically screened Coulomb interaction, supporting a fully electronically driven isostructral insulator-to-metal transition. We thus conclude that the ultrafast band structure renormalization is caused by photoexcitation of carriers from localized V 3d valence states, strongly changing the screening \emph{before} significant hot-carrier relaxation or ionic motion has occurred.
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