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

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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.