Thesis defense of Jonah Elias Nitschke

Magnetic order in low-dimensional materials offers exciting opportunities for spintronic, quantum, and next-generation information storage applications. Among layered magnetic crystals, the transition-metal thiophosphates (MPS3, with M = Mn, Fe, Co, Ni) stand out for their air stability, chemical versatility, and diverse magnetic ground states, making them an ideal platform for studying the interplay between spin, charge, and lat}ce degrees of freedom. This thesis combines different photoemission spectroscopy techniques, including X-ray photoelectron spectroscopy (XPS), angle-resolved photoelectron spectroscopy (ARPES), and time-resolved ARPES (trARPES), with first-principles calculations to investigate the electronic structure, quasiparticle dynamics, and tunability of four representative MPS3 compounds. In the first part, XPS and ARPES establish the intrinsic electronic properties, revealing complex valence-band structures with dispersive and flat bands, material-dependent orbital hybridisation, and momentum-dependent intensity variations. Using trARPES on FePS3, we identify and characterise two distinct d-d transitions, determine their lifetimes and momentum fingerprints, and demonstrate the method's ability to follow local multiplet excitations in momentum space. In the second part, we explore tunability via molecular adsorption and alkali-metal intercalation. Photoemission orbital tomography on pentacene monolayers on FePS3 and NiPS3 reveals well-ordered, physisorbed layers, providing a baseline for studies with stronger donor-acceptor systems. Lithium and caesium intercalation show element-specific doping behaviour, oxidation-state changes, and orbital-selective band modifications, highlighting the potential for controlled band-structure engineering. Overall, this work presents a detailed study of the electronic ground state of four representative MPS3 compounds, extends trARPES to multiplet excitations by investigating electron dynamics in FePS3, and provides first insights into targeted modification through molecular adsorption and alkali-metal intercalation, demonstrating the versatility and potential of this material class.