Join the OSA Ultrafast Optical Phenomena Technical Group for this special virtual event featuring Prof. Keshav M. Dani of the Femtosecond Spectroscopy Unit at the Okinawa Institute of Science and Technology in Japan.
About a decade ago, the discovery of monolayers of transition metal dichalcogenides opened a new frontier in the study of optically excited states in semiconductors. These materials exhibit a plethora of robust excitonic states – bound quasiparticle pairs of electrons and holes, such as bright excitons, momentum- and spin-forbidden dark excitons, and hot excitons. While optics-based experiments can access bright excitons, measuring dark excitons requires a momentum-resolving technique like ARPES – a decades-old grand challenge.
Accessing excitons with ARPES is not just conceptually unclear, but also technically challenging. One needs to study micron-scale samples of 2D materials, with ultrafast time-resolution, using XUV photons. Prof. Dani will discuss the progress in his lab towards these goals utilizing ultrafast photoemission techniques with spatial- and momentum-resolution [1, 2] that we have also used to learn valuable information in a variety of other materials systems [3, 4, 5].
Hot-Topic Literature on Ultrafast ARPES Microscopy from the Dani Group:
 J. Madeo, M. K. L. Man, et al. Science 370, 1199 (2020) https://doi.org/10.1126/science.aba1029
 M. K. L. Man, J. Madeo, et al. Science Advances 7, eabg0192 (2021) https://doi.org/10.1126/sciadv.abg0192
 T. Doherty, A. Winchester, et al. Nature 580, 360 (2020) https://doi.org/10.1038/s41586-020-2184-1
 E. L. Wong, et al. Science Advances 4, eaat9722 (2018) https://advances.sciencemag.org/content/4/9/eaat9722
 M. K. L. Man, et al. Nature Nanotechnol. 12, 36 (2017) https://www.nature.com/articles/nnano.2016.183