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Summary: Arguably, some of the most intriguing phenomena in contemporary condensed matter research can be observed in systems of “reduced” dimensions. In cases where electrons are not allowed to propagate freely in all three spatial directions, a newfound interplay with other electrons and other collective excitations can often be observed. The confinement of the electrons can thus lead to altered electronic properties or, in extreme cases, completely different phase behavior. For instance, the results can range from electronic states with massless Dirac fermions to potent pairing mechanisms for unconventional superconductivity. Ultimately, the implications of said “confinement” would depend on the material the electrons propagate in and the other degrees of freedom it enables and inhabits. This thesis is concerned with forming and studying such systems of “reduced” dimensions and the physical phenomena they exhibit. The work is based on six research papers covering various topics, materials, and experimental techniques. Three papers examine the physical structure of state-of-the-art quantum materials and pathways to modify and control their behavior and quality. The remaining three focus on electron interactions with collective modes of excitation, both in van der Waals materials and in ferromagnetic and antiferromagnetic structures and heterostructures. Sammendrag: Flere underlige og fascinerende fysiske fenomener i moderne materialfysikk forekommer i systemer med «redusert» dimensjonalitet: altså en- eller to-dimensjonale materialer. I situasjoner der elektronene ikke står fritt til å bevege seg i alle tre romlige retninger, vil nettopp denne begrensingen av elektronenes «frihet» kunne føre til nye interaksjoner – enten innbyrdes mellom elektronene selv, eller med andre frihetsgrader i systemet. Resultatene kan variere fra mindre eller moderate endringer materialets elektroniske egenskaper. For eksempel, at de strømledende elektronene som blir tyngre eller tilnærmet «masseløse», eller mer drastiske endringer, som faseovergang til «superledning» med netto null elektrisk motstand. Denne avhandlingen bygger på seks forskningsartikler som alle omhandler materialsystemer i «reduserte» dimensjoner, og de fysiske fenomenene som opptrer i disse. Tre av arbeidene omhandler todimensjonale kvantematerialer, og setter søkelys på hvordan å utforme eller manipulere disse for å optimalisere materialkvaliteten, eller skreddersy strømledningsoppførselen deres. De siste tre arbeidene omhandler samvirkningen mellom elektroner og andre, delokaliserte energieksitasjoner, som gittervibrasjoner («fononer») og/eller magnetiske spinbølger («magnoner»).

Ultraviolet-light-induced changes to the nucleobase thymine deposited onto a MoS2 surface were studied using photoelectron spectroscopy and first-principles calculations. These measurements suggest changes in the molecular structure indicated by changes in core electron binding energies. The experimental work has been interpreted by means of ab initio calculations using coupled cluster singles and doubles (CCSD) linear response theory. Contrary to the expected behavior, i.e., the dimerization of two thymine molecules into a pyrimidine dimer, a shift between two tautomeric forms was observed upon UV-exposure. Exposure to ionizing radiation is known to induce damage in many biological molecules, and the present work gives additional insight into its effects on thymine, the interactions of the molecules, and finally how certain UV photoproducts may be avoided.