CM Seminar - Ultrafast dynamics of excitons, electrons and phonons in momentum space

25 Feb2021

Speaker: Ralph Ernstorfer, Fritz Haber Institute of the Max Planck Society

Time: Feb 25, 2021 :: 10:00AM - 11:00AM



Ultrafast dynamics of excitons, electrons and phonons in momentum space

Abstract: 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 WSe2 [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]. I will sketch the capability of multidimensional photoemission spectroscopy of providing orbital information [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].

[1]         M. Puppin et al., Rev. Sci. Inst. 90, 23104 (2019).
[2]         J. Maklar et al., Rev. Sci. Inst. 91, 123112 (2020).
[3]         S. Dong et al., arXiv:2012.15328 (2020).
[4]         R. Bertoni et al., Phys. Rev. Lett. 117, 277201 (2016).
[5]         D. Christiansen et al., Phys. Rev. B 100, 205401 (2019).
[6]         M. Dendzik et al., Phys. Rev. Lett. 125, 096401 (2020).
[7]         S. Beaulieu et al., Phys. Rev. Lett. 125, 216404 (2020).
[8]         L. Waldecker et al., Phys. Rev. Lett. 119, 036803 (2017).

Short Bio: Study of Physics at Technical University Munich; PhD (2004) at Free University Berlin & Hahn-Meitner Institut under the supervision of Frank Willig; postdoc at the University of Toronto (with Dwayne Miller) and the Max Planck Institute for Quantum Optics in Garching (with Ferenc Krausz and Reinhard Kienberger); since 2010: head of the Max Planck Research Group Structural & Electronic Surface Dynamics at the Fritz-Haber-Institut; since 2016: Consolidator Grant of the European Research Council (ERC)

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