Speaker
Description
Angle-resolved photoemission spectroscopy (ARPES) has evolved into a powerful platform for probing not only the equilibrium electronic structure but also the ultrafast dynamics of correlated quantum materials. In this talk, I will highlight how time-resolved momentum microscopy based on high-repetition-rate fs-XUV sources enables full–Brillouin-zone mapping of nonequilibrium electronic structure with tunable energy and time resolution [1], opening new pathways to investigate elementary and composite excitations in low-dimensional systems.
Using this approach, I will present recent results on van der Waals antiferromagnets, focusing on the interplay between orbital degrees of freedom, magnetic order, and ultrafast dynamics. First, I will discuss the electronic structure of the layered semiconductor CrPS₄, where ARPES combined with DFT reveals a ligand-to-metal charge-transfer gap and distinct hybridization regimes within the Cr 3d manifold, linking weakly hybridized t₂g states to magnetic order and strongly hybridized eg states to optically active orbital excitations [2].
Building on this microscopic framework, I will then show how time-resolved ARPES provides access to orbital d–d excitations in FePS₃ through their momentum-dependent photoemission signatures [3]. Although these excitations are intrinsically local and not dispersive in a band-structure sense, their spectral fingerprints exhibit a well-defined structure in momentum space. By resolving their dynamics, we identify fundamentally different relaxation pathways for spin-allowed and spin-forbidden transitions, governed by exchange interactions and spin–orbit coupling.
Together, these results establish momentum-resolved photoemission as a versatile approach to uncover the signatures of ultrafast orbital excitations and their coupling to other degrees of freedom [4], paving the way toward a microscopic understanding of composite excitations in correlated quantum materials.
[1] K. Schiller, et al. Scientific Reports 15:3611 (2025). doi:10.1038/s41598-025-86660-1
[2] L. Sternemann, L., et al. arXiv (2025). doi:10.48550/arxiv.2511.17403
[3] J. E. Nitschke, et al. Newton 1, 100019 (2025). doi:10.1016/j.newton.2025.100019
[4] F. Mertens, Advanced Materials 35, 2208355 (2023). DOI:10.1002/adma.202208355