Time-resolved photoemission: From bandstructure to orbital movies

DIPC Seminars

Ulrich Höfer
University of Marburg, Germany
Hybrid Seminar: Donostia International Physics Center
Ricardo Díez Muiño
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Time-resolved photoemission: From bandstructure to orbital movies

Time-resolved photoemission combines femtosecond pump-probe techniques with angle-resolved photoelectron spectroscopy (ARPES). While the target of many early investigations was the dynamics of surface electronic states, recent developments enable the method to basically track electron motion in momentum space on ultrafast time scales. This capability allows to explore ultrafast electronic processes of a variety of novel quantum materials by clearcut experiments.

In this talk, I will briefly introduce the state-of-the-art of the method and discuss a couple of examples from our recent work. These include bandstructure movies of the intraband acceleration of electrons in topologically protected Dirac surface states [1,2], of the birth and collapse of Floquet- Bloch states [3], and of the formation of momentumforbidden and spin-forbidden dark excitons in TMDC monolayers [4]. Finally, I will outline the perspectives of photoemission orbital tomography [5] to take slow-motion movies of molecular orbitals while they are driven by lightwaves.

[ 1] J. Reimann et al., “Subcycle observation of lightwavedriven Dirac currents”, Nature 562, 396 (2018)
[2] C. P. Schmid et al., “Tunable non-integer high-harmonic generation in a topological insulator”, Nature 593, 385 (2021)
[3] S. Ito et al., “Ultrafast birth, rise, and collapse of a Floquet-Bloch band structure”, Nature 616, 696 (2023)
[4] R. Wallauer et al., “Momentum-resolved exciton formation dynamics in monolayer WS2 ”, Nano. Lett. 21, 5867 (2021)
[5] R. Wallauer et al., “Tracing orbital images on ultrafast time scales”, Science 371, 1056 (2021)

Zoom: https://dipc-org.zoom.us/j/93732219269