Ralph Ernstorfer4,1,Shuo Dong1,Tommaso Pincelli1,Samuel Beaulieu1,Maciej Dendzik1,Julian Maklar1,Daniela Zahn1,Helene Seiler1,Michele Puppin2,1,Alexander Neef1,Lutz Waldecker3,Martin Wolf1,Laurenz Rettig1
Fritz Haber Institute of the Max Planck Society1,EPFL2,RWTH Aachen University3,Technical University Berlin4
Ralph Ernstorfer4,1,Shuo Dong1,Tommaso Pincelli1,Samuel Beaulieu1,Maciej Dendzik1,Julian Maklar1,Daniela Zahn1,Helene Seiler1,Michele Puppin2,1,Alexander Neef1,Lutz Waldecker3,Martin Wolf1,Laurenz Rettig1
Fritz Haber Institute of the Max Planck Society1,EPFL2,RWTH Aachen University3,Technical University Berlin4
The dynamics of quasi-particles in non-equilibrium states of matter reveal the underlying microscopic coupling between electronic, spin and vibrational degrees of freedom. We aim for a quantum-state-resolved picture of coupling on the level of quasi-particle self-energies, which goes beyond established ensemble-average descriptions, and which requires ultrafast momentum-resolving techniques. The dynamics of electrons and excitons are measured with four-dimensional time- and angle-resolved photoelectron spectroscopy (trARPES), featuring a high-repetition-rate XUV laser source and momentum microscope detector [1,2]. I will discuss exciton and electron dynamics in the semiconducting transition metal dichalcogenide WSe<sub>2</sub> [3,4,5,6]. We retrieve fundamental exciton properties like the binding energy and the exciton-phonon interaction and reconstruct the real-space excitonic wave function via Fourier transform of the photoelectrons’ momentum distribution [3]. The extension of the approach to van der Waals heterostructures reveals the competition between charge and energy/exciton transfer process as well as a previously not observed intraband Meitner-Auger energy transfer process [7]. The complementary view of ultrafast phonon dynamics is obtained through femtosecond electron diffraction. The elastic and inelastic scattering signal reveals the temporal evolution of vibrational excitation of the lattice and momentum-resolved information of transient phonon populations [8].<br/>References:<br/>[1] M. Puppin et al., Rev. Sci. Inst. 90, 23104 (2019).<br/>[2] J. Maklar et al., Rev. Sci. Inst. 91, 123112 (2020).<br/>[3] S. Dong et al., Natural Sciences 1, e10010 (2021).<br/>[4] R. Bertoni et al., Phys. Rev. Lett. 117, 277201 (2016).<br/>[5] D. Christiansen et al., Phys. Rev. B 100, 205401 (2019).<br/>[6] M. Dendzik et al., Phys. Rev. Lett. 125, 096401 (2020).<br/>[7] Dong et al., arXiv:2108.06803 (2021).<br/>[8] L. Waldecker et al., Phys. Rev. Lett. 119, 036803 (2017).