Far-from-Equilibrium Quasiparticle Dynamics in Graphene

von Marten Düvel
Dissertation
Datum der mündl. Prüfung:2022-11-25
Erschienen:2023-01-17
Betreuer:Prof. Dr. Stefan Mathias
Gutachter:Prof. Dr. Stefan Mathias
Gutachter:Prof. Dr. Martin Wenderoth
Zum Verlinken/Zitieren: http://dx.doi.org/10.53846/goediss-9664

 

 

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Comprehending far-from-equilibrium many-body interactions is one of the major goals of current ultrafast condensed matter physics research. Here, a particularly interesting but barely understood situation occurs during a strong optical excitation, where the electron and phonon systems can be significantly perturbed and the quasiparticle distributions cannot be described with equilibrium functions. In this thesis, we use time- and angle-resolved photoelectron spectroscopy (trARPES) to study such far-from-equilibrium many-body interactions for the prototypical material graphene by evaluating the low-energy non-equilibrium quasiparticle self-energy at the femtosecond timescale. The low-energy quasiparticle response, however, is at first inaccessible due to resolution artifacts caused by the spectrally our broad XUV probe pulses, which are unavoidable due to the time-bandwidth-product. Therefore, we apply a Lucy-Richardson deconvolution algorithm (LRD) to the ARPES spectra. Furthermore, we introduce rigorous benchmarking of the LRD to assure physical-meaningful results. To deliver angle-resolved photoemission spectroscopy (ARPES) data in the necessary quality for this LRD approach, we built a trARPES setup with an extreme ultraviolet (XUV) probe source in this thesis. This XUV probe source can be switched between an energy-resolution optimized beamline and time-resolution optimized beamline. With this experiment, we find remarkable transient renormalizations of the quasiparticle self-energy caused by the photo-induced non-equilibrium conditions, which are in accordance with first-principles theoretical modeling. These observations can be understood by ultrafast scatterings between far-from-equilibrium electrons and strongly-coupled optical phonons, which signifies the crucial role of ultrafast non-equilibrium dynamics on many-body interactions. Our results advance the understanding of many-body physics in extreme conditions, which is important for any endeavor to optically manipulate or create emergent states of matter.
Keywords: graphene, trARPES, nonequilibrium electron−phonon interaction, quasiparticle self-energy, Lucy−Richardson deconvolution algorithm, density functional theory
 
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