Attosecond time-resolved streaking spectroscopy as a probe of strong field effects at the solid-vacuum interface of layered materials

固体-真空界面附近的强电磁场可以动态改变表面性质，并可能在亚周期时间尺度上控制界面电荷转移过程。实现这种强场控制既需要完全了解原子长度尺度上的实际场分布，也需要了解发生在这种大规模摄动多体系统中的复杂过程。目前，界面附近原子尺度的局部动态场分布是未知的。这个问题在本项目中得到解决，该项目旨在提高对控制界面处强红外场作用的基本过程的理解，并解决有关光电过程动力学的开放问题。为了实现这些目标，采用了固体表面的阿秒条纹光谱。在单阿秒XUV脉冲激励下，光电子通过衬底-真空界面传播，并与衬底-真空界面相互作用，同时产生强红外条纹场。决定观测到的光发射延迟的基本机制和过程仍在争论中，目前还没有完整的理论模型。在这个项目中，过渡金属二硫族化物形成层状范德华晶体和其他层状材料，以原子精度定位发射的核心能级光电子的起源。迄今为止的实验表明，靠近界面的原子尺度局域场分布对光电子条纹化有很强的影响。使用这种层状材料和单层范德瓦尔斯晶体的进一步实验将为这一工作假设提供检验。对条纹效应的角度依赖性的系统研究将提供有关局部条纹场影响的基本信息。

Strong electromagnetic fields in the vicinity of the solid-vacuum interface can dynamically change surface properties and might serve to control interfacial charge transfer processes on a sub-cycle time-scale. The implementation of such strong field control requires both, the complete knowledge of the actual field distribution on an atomic length scale and the understanding of the complex processes occurring in this massively perturbed many-body system. Presently the atomic-scale local dynamic field distribution in the vicinity of the interface is unknown. This issue is addressed in the present project that aims to improve the understanding of the fundamental processes governing the action of strong IR fields at interfaces and also addresses open questions concerning the dynamics of the photoemission process. To achieve these goals attosecond streaking spectroscopy at solid surfaces is employed. Photoelectrons excited by a single attosecond XUV pulse propagate through the substrate-vacuum interface and interact with the simultaneously present intense IR streaking field. The fundamental mechanisms and processes determining the observed delays in photoemission are still under debate and no complete theoretical model is available yet. In this project transition metal dichalcogenides forming layered van der Waals crystals and other layered materials are employed to localize the origin of the emitted core level photoelectrons with atomic precision. The experiments conducted up to now indicate that the photoelectron streaking is strongly affected by the atomic scale local field distribution close to the interface. Further experiments using such layered materials and single van der Waals crystal monolayers will provide a test of this working hypothesis. The systematic investigation of the angular dependence of the streaking effect shall provide essential information on the impact of local streaking fields.