Exploring electron-phonon interactions and coherent-phonon control of quantum materials using frequency-domain ARPES

频域角度分辨光电子能谱(FDARPES)是一种基于时间分辨ARPES(TrARPES)信号傅立叶分析的技术，是研究非平衡系统中电子-声子相互作用的一种很有前途的实验工具。除了揭示与相干声子相互作用引起的电子结构的瞬时变化(晶格的同相振动)外，它还被认为是一种直接确定电子-声子耦合矩阵元的新途径，并且能够以前所未有的详细程度解决能带自旋分裂的瞬时变化。尽管有这些独特的特点，FDARPES到目前为止只在两个实验研究中得到了应用。这个项目的目标是确定FDARPES在多大程度上可以作为一种诊断工具来研究量子物质中的光驱动现象。具体地说，在实验和理论相结合的工作中，我们的目标是确定FDARPES在系统和定量研究凝聚态中的电子-声子相互作用、自旋-轨道耦合和相干-声子退相方面的能力。我们将对层状过渡金属二卤化物TD-MoTe2和1T‘-MoTe2进行高质量的FDARPES实验。这些化合物显示出丰富的相干声子光谱，这是FDARPES测量的重要前提。此外，这两个同素异形体通过一个可以由光驱动的相变来连接。我们将从FDARPES强度的分析中探索FDARPES是否适合直接提取电子-声子和声子-声子耦合矩阵元。我们的进一步目标是建立一个通过激发相干剪切声子模引起的瞬时反转对称破缺来控制自旋分裂和Rashba-Dresselhaus效应的理论基础。实验研究将得到(I)最先进的电子-声子相互作用的第一性原理计算；(Ii)研究相干声子的形成和退相的新的理论和计算框架的发展。

Frequency-domain angle-resolved photoemission spectroscopy (FDARPES) – a technique based on the Fourier analysis of time-resolved ARPES (TRARPES) signals – is emerging as a promising experimental tool to investigate electron-phonon interactions in systems out of equilibrium. Beside revealing transient changes of the electronic structure due to the interaction with coherent phonons (in-phase vibrations of the crystalline lattice), it has been proposed as a new route to directly determine electron-phonon coupling matrix elements, and it can resolve transient changes in the spin-splitting of bands with unprecedented level of detail. Despite these unique characteristics, FDARPES has thus far seen application only in two experimental studies thus far. Goal of this project is to establish to which extent FDARPES may serve as a diagnostic tool to investigate light-driven phenomena in quantum matter. Specifically, in a combined experimental and theoretical effort, we aim at determining the capabilities of FDARPES in studying electron-phonon interactions, spin-orbit coupling, and coherent-phonon dephasing in condensed matter in a systematic and quantitative manner. We will conduct high-quality FDARPES experiments for the layered transition-metal dichalcogenides Td-MoTe2 and 1T’-MoTe2. These compounds exhibit a rich spectrum of coherent phonons, an important prerequisite for FDARPES measurements. Additionally, the two allotropes are connected by a phase transition which can be driven by light. We will explore the suitability of FDARPES to directly extract electron-phonon and phonon-phonon coupling matrix elements from the analysis of FDARPES intensities. We further aim to establish a rationale to control spin-splitting and the Rashba-Dresselhaus effect through the transient inversion-symmetry breaking induced by the excitation of coherent shear-phonon modes. Experimental investigations will be complemented by (i) state-of-the-art first-principles calculations of the electron-phonon interactions; (ii) the development of a new theoretical and computational framework to study the formation and dephasing of coherent phonons.