Interaction of many-body systems with ultrashort light pulses may lead to emergent phenomena away from equilibrium like photo-stabilization of hidden phases or ultrafast phase transitions. These processes are characterized by pronounced changes in the electronic structure and occupation of electronic states. Recent advances in ultrafast spectroscopy allow direct probing of the underlying fundamental steps and provide a mechanistic understanding of transfer of energy from the electronic system into nuclear motions.
Here I will discuss recent advances to probe such transient changes by a table-top 500 kHz HHG based XUV laser source enabling excited state band mapping throughout the complete Brillouin zone by time-resolved photoemission spectroscopy (trARPES) . Within the same setup we have implement a hemispherical analyzer and a momentum microscope and we highlight the advantages and limitations of both instruments based on exemplary trARPES measurements of bulk WSe2, depending on pump- and probe-induced space-charge effects, detection efficiency, photoelectron count rates . Such trARPES experiments provide detailed insights into the photo-induced phase transition in quasi-1D metal nanowires on In/Si(111) , the ultrafast Lifshitz transition in MoTe2 , non-equilibrium CDW dynamics in TbTe3  and the spatial extend of the excitonic wave function in WSe2 , which will be discussed as examples.
 M. Puppin et al., Rev. Sci. Instr. 90, 023104 (2019)
 J. Makler et al., Rev. Sci. Instr. 91, 123112 (2020)
 C.W. Nicholson et al., Science 362, 821 (2018)
 S. Beaulieu et al., Science Advances (accepted, arXiv:2003.04059)
 J. Makler et al., Nature Communications (accepted, arXiv:2011.03230)
 S. Dong et al., arXiv:2012.15328
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Meeting ID: 954 5947 0122
Serguei Molodtsov / Gabriella Mulá-Mathews