Non-equilibrium carrier dynamics in proximity-coupled graphene

外延石墨烯（EG）和SiC（0001）之间的界面是一个有限的空间，允许生长具有迷人电子特性的新型二维材料（2DM），包括Mott绝缘体，Rashba材料，超导体和可能的拓扑绝缘体。虽然这些2DM本身就很有趣，但它们也提供了一个有趣的平台来研究它们上面的石墨烯层上的各种邻近诱导效应。本项目的主要目的是研究插层2DM对石墨烯层的非平衡载流子动力学（NECD）的影响与时间和角度分辨光电子能谱（tr-ARPES）。除了众所周知的平衡邻近诱导效应如邻近诱导自旋轨道耦合和超导性外，EG的NECD还将受到额外的非平衡邻近诱导效应如EG/2DM界面上的超快电荷转移和光诱导相变的影响。在解决这些主要目标之前，我们建议使用限制外延来稳定由Bi，Sb，或Sn在EG/SiC（0001）界面上具有拓扑非平凡的电子性质，从而更好地理解结构缺陷对EG/SiC（0001）NECD的影响。详细地说，这个项目将解决以下悬而未决的问题：我们可以稳定的蜂窝层与EG和SiC（0001）之间的界面拓扑非平凡的电子特性？结构缺陷对石墨烯的NECD有什么影响？这种影响是否会在存在近耦合2DM时发生变化？EG和邻近耦合2DM之间是否存在超快电荷转移？我们能通过掺杂和屏蔽来控制各种EG/2DM异质结构的NECD吗？邻近耦合拓扑绝缘体、莫特绝缘体或超导体的存在如何影响石墨烯的NECD？2DM中可能的光致相变对EG的NECD有什么影响？为了回答这些问题，我们将激发不同的EG/2DM异质结构与波长可调谐的可见光，红外，或中红外飞秒泵浦脉冲和探测NECD的异质结构作为能量，动量和时间的函数与tr-ARPES。为此，极紫外探测脉冲将从样品中发射光电子。这些光电子将根据它们的发射角和动能用半球形分析器分散，使得在二维检测器上成像的光电流将直接揭示EG/2DM异质结构的能带结构内的非平衡载流子分布的快照。改变泵浦探测延迟将使我们能够记录NECD的慢动作电影以及可能的光致能带结构变化。

The interface between epitaxial graphene (EG) and SiC(0001) is a confined space that allows for the growth of novel two-dimensional materials (2DMs) with fascinating electronic properties including Mott insulators, Rashba materials, superconductors, and possibly topological insulators. While these 2DMs are interesting in their own right, they also offer an intriguing platform to investigate various proximity-induced effects on the graphene layer that rests on top of them. The main objective of the present project is to investigate the influence of the intercalated 2DM on the non-equilibrium carrier dynamics (NECD) of the graphene layer with time- and angle-resolved photoemission spectroscopy (tr-ARPES). Aside from the well-known equilibrium proximity-induced effects such as proximity-induced spin-orbit coupling and superconductivity, the NECD of EG will be influenced by additional non-equilibrium proximity-induced effects such as ultrafast charge transfer across the EG/2DM interface and photo-induced phase transitions.Before addressing these main objectives, we propose to use confinement epitaxy to stabilize honeycomb layers made of Bi, Sb, or Sn with topologically non-trivial electronic properties at the interface between EG and SiC(0001), and to obtain a better understanding of the influence of structural defects on the NECD of EG/SiC(0001). In detail, this project will address the following open questions:Can we stabilize honeycomb layers with topologically non-trivial electronic properties at the interface between EG and SiC(0001)?What is the influence of structural defects on the NECD of graphene? Does this influence change in the presence of a proximity-coupled 2DM?Is there ultrafast charge transfer between EG and the proximity-coupled 2DM?Can we control the NECD of various EG/2DM heterostructures via doping and screening?How are the NECD of graphene affected by the presence of a proximity-coupled topological insulator, Mott insulator, or superconductor?What is the influence of a possible photo-induced phase transition in the 2DM on the NECD of EG?In order to answer these questions, we will excite different EG/2DM heterostructures with wavelength-tunable visible, infrared, or mid-infrared femtosecond pump pulses and probe the NECD of the heterostructure as a function of energy, momentum, and time with tr-ARPES. For that purpose, an extreme ultraviolet probe pulse will eject photoelectrons from the sample. These photoelectrons will be dispersed according to their emission angle and kinetic energy with a hemispherical analyzer such that the photocurrent imaged on a two-dimensional detector will directly reveal a snapshot of the non-equilibrium carrier distribution within the band structure of the EG/2DM heterostructure. Varying the pump-probe delay will then allow us to record slow-motion movies of the NECD as well as possible photo-induced band structure changes.