Julian has defended his thesis with distinction. Congratulations and all the best for your future!

Singlet fission may boost photovoltaic efficiency by transforming a singlet exciton into two triplet excitons and thereby doubling the number of excited charge carriers. The primary step of singlet fission has been disputed for decades and several mechanisms have been proposed. Using time- and angle-resolved photoemission spectroscopy, we record an ultrafast movie of the formation and fission of excitons in crystalline pentacene. Our results reveal the orbital character of the excited states providing unprecedented insight into the mechanism of the singlet fission process.
Neef et al., Nature 616, 275 (2023). See also related News & Views by Musser and Stern.

Understanding phase competition and phase separation in quantum materials requires access to the spatiotemporal dynamics of electronic ordering phenomena on a micro- to nanometer length- and femtosecond timescale. While time- and angle-resolved photoemission (trARPES) experiments provide sensitivity to the femtosecond dynamics of electronic ordering, they typically lack the required spatial resolution. Here, we demonstrate ultrafast dark-field photoemission microscopy (PEEM) using a momentum microscope, providing access to ultrafast electronic order on the microscale. We investigate the prototypical Charge-Density Wave (CDW) compound TbTe₃ in the vicinity of a buried crystal defect, demonstrating real- and reciprocal-space configurations combined with a pump-probe approach.
For more details, including a recording of the presentation at SPIE Photonics West 2023, see Proc. [more...]

The electronic band structure and crystal structure are the two complementary identifiers of solid-state materials. Although convenient instruments and reconstruction algorithms have made large, empirical, crystal structure databases possible, extracting the quasiparticle dispersion (closely related to band structure) from photoemission band mapping data is currently limited by the available computational methods. To cope with the growing size and scale of photoemission data, here we develop a pipeline including probabilistic machine learning and the associated data processing, optimization, and evaluation methods for band-structure reconstruction, leveraging theoretical calculations. The pipeline reconstructs all 14 valence bands of a semiconductor and shows excellent performance on benchmarks and other materials datasets. The reconstruction uncovers previously inaccessible momentum-space structural information on both global and local [more...]

Sang successfully defended his PhD thesis in Dec. 2022. Congratulations and best wishes for your future!