二维VSe $_2$中绝缘体-金属转变的超快触发
Ultrafast triggering of insulator-metal transition in two-dimensional VSe$_2$
摘要：
在二维（2D）极限下组装过渡金属二硫属化物（TMDC）是一种很有前途的方法，用于定制新兴的物质状态，如超导性或电荷密度波（CDW）。单层（SL）VSe $_2$在这方面突出，因为除了在费米能级处具有各向异性间隙的绝缘相之外，它还表现出与体相相比具有更高转变温度的强烈增强的CDW转变，从而导致材料中预期的2D铁磁性的抑制。在这里，我们调查的电子和晶格自由度的相互作用，支持这些电子阶段在SL VSe $_2$使用超快泵浦-探测光电子能谱。在绝缘状态下，我们观察到一个光诱导的能隙关闭的时间尺度为480 fs，我们解开随之而来的热载流子动力学。因此，我们的工作揭示了SL VSe $_2$中的相变是由电子-晶格耦合驱动的，并展示了用光控制2D材料中的电子相的潜力。
英文摘要：
Assembling transition metal dichalcogenides (TMDCs) at the two-dimensional (2D) limit is a promising approach for tailoring emerging states of matter such as superconductivity or charge density waves (CDWs). Single-layer (SL) VSe$_2$ stands out in this regard because it exhibits a strongly enhanced CDW transition with a higher transition temperature compared to the bulk in addition to an insulating phase with an anisotropic gap at the Fermi level, causing a suppression of anticipated 2D ferromagnetism in the material. Here, we investigate the interplay of electronic and lattice degrees of freedom that underpin these electronic phases in SL VSe$_2$ using ultrafast pump-probe photoemission spectroscopy. In the insulating state, we observe a light-induced closure of the energy gap on a timescale of 480 fs, which we disentangle from the ensuing hot carrier dynamics. Our work thereby reveals that the phase transition in SL VSe$_2$ is driven by electron-lattice coupling and demonstrates the potential for controlling electronic phases in 2D materials with light.
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