用阿秒光谱解释局域激子的原子和体的纠缠性质
Unravelling the intertwined atomic and bulk nature of localised excitons by attosecond spectroscopy
摘要：
大多数技术上感兴趣的半导体和绝缘体的电光特性由称为激子的电子空穴准粒子的存在所支配。这些氢类准粒子的操纵在量子力学中，已经在激子的名称下引起了极大的兴趣，预计在各种应用中具有巨大的潜力，包括光电子学和光子学。在先进技术应用中利用激子的关键一步是详细了解它们的动力学性质。然而，在几个飞秒和阿秒的时间尺度上展开的超快过程，鉴于电子设备向千兆赫制度的期望扩展的主要相关性，仍然在很大程度上未被探索。在这里，我们应用阿秒瞬态反射光谱在一个连续的两个焦点的几何形状和观察亚飞秒动力学的核心水平激子在体氟化镁$_2$单晶。通过我们独特的设置，我们可以访问绝对相位延迟，从而可以与基于Wannier-Mott模型的理论计算进行明确的比较。我们的研究结果表明，激子令人惊讶地表现出双重原子和固体的字符，表现出自己在不同的时间尺度。虽然前者是负责飞秒光学斯塔克效应，后者占主导地位的阿秒激子响应和起源与晶体的相互作用。激子本地化的作用的进一步调查证明，大量的字符仍然存在强烈本地化的准粒子，并允许我们设想一个新的路线来控制激子动力学在接近的拍赫兹制度。
英文摘要：
The electro-optical properties of most semiconductors and insulators of technological interest are dominated by the presence of electron-hole quasiparticles called excitons. The manipulation of these hydrogen-like quasi-particles in dielectrics, has received great interest under the name excitonics that is expected to be of great potential for a variety of applications, including optoelectronics and photonics. A crucial step for such exploitation of excitons in advanced technological applications is a detailed understanding of their dynamical nature. However, the ultrafast processes unfolding on few-femtosecond and attosecond time scales, of primary relevance in view of the desired extension of electronic devices towards the petahertz regime, remain largely unexplored. Here we apply attosecond transient reflection spectroscopy in a sequential two-foci geometry and observe sub-femtosecond dynamics of a core-level exciton in bulk MgF$_2$ single crystals. With our unique setup, we can access absolute phase delays which allow for an unambiguous comparison with theoretical calculations based on the Wannier-Mott model. Our results show that excitons surprisingly exhibit a dual atomic- and solid-like character which manifests itself on different time scales. While the former is responsible for a femtosecond optical Stark effect, the latter dominates the attosecond excitonic response and originates by the interaction with the crystal. Further investigation of the role of exciton localization proves that the bulk character persists also for strongly localised quasi-particles and allows us to envision a new route to control exciton dynamics in the close-to-petahertz regime.
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