Samuel Beaulieu
Université de Bordeaux – CNRS – CEA, CELIA, UMR5107, F33405, Talence, France

” Ultrafast Multidimensional Photoemission Spectroscopy of 2D Materials “

Angle-resolved photoemission spectroscopy (ARPES) is arguably the most direct and powerful technique to measure electronic eigenvalues (band structure) of solids. Combining pump-probe scheme (using femtosecond XUV probe pulses) with ARPES, allows to measure the dynamical modification of populations, their scattering pathways, as well as modification of many-body interactions following photoexcitation of solids, on unprecedently fast timescales. In this talk, I will present three recent key findings that we made on two-dimensional transition metal dichalcogenides (TMDCs) using this technique:

a) the demonstration that all key microscopic quantities of an excitonic state are encoded in the multidimensional photoemission signal: the spatial distribution of the excitonic wave function, its binding energy, and its lifetime, here exemplified for bulk 2H-WSe2 [1].

b) the first demonstration of light-induced Lifshitz transition. Indeed, we demonstrate that the photoinduced dynamical modification of electronic correlations can lead to a transient and reversible modification of the Fermi surface topology in the type-II Weyl semimetal Td-MoTe2 [2].

c) the introduction of novel observables in ARPES allowing to go beyond band structure mapping and access information about the momentum-resolved Bloch wave function [3,4].

I will also discuss the new experimental setup that is currently under development at CELIA that will allow using these new observables [3,4] to investigate ultrafast topological phase transitions in quantum materials.

[1] Dong et al., Natural Sciences 1, e10010 (2021)
[2] Beaulieu et al., Science Advances 7, eabd9275 (2021)
[3] Beaulieu et al., Physical Review Letters 125, 216404 (2020)
[4] Schüler, …, and Beaulieu, Physical Review X 12, 011019 (2022)