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TY - THES AU - Jin, Keda TI - Probing electric and magnetic order in 2D van der Waals heterostructures with scanning tunneling methods PB - RWTH Aachen University VL - Dissertation CY - Aachen M1 - RWTH-2025-10153 SP - 1 Online-Ressource : Illustrationen PY - 2025 N1 - Veröffentlicht auf dem Publikationsserver der RWTH Aachen University 2026 N1 - Dissertation, RWTH Aachen University, 2025 AB - Van derWaals (vdW) heterostructures offer a versatile platform for engineering exotic quantum states of matter. These states arise at the interfaces where layers are weakly coupled by vdW interactions. Scanning tunnelling microscopy (STM) provides a powerful tool to probe these interfaces, offering a microscopic understanding of these exotic states. However, STM requires pristine sample surfaces, often incompatible with conventional polymer-based transfer techniques. The first step of this thesis involved developing a novel assembly method to fabricate clean heterostructures by avoiding direct contact between the polymer and the materials. This approach enables the creation of air-sensitive heterostructures with clean interfaces and surfaces, which is compatible with STM investigations. Using this method, three systems were studied: 1T-NbSe₂ on 2H-NbSe₂, graphene on 1TNbSe₂/ 2H-NbSe₂, and CrSBr on 2H-NbSe₂. In the first system, the √13×√13 charge density wave (CDW) in 1T-NbSe₂ led to localized states within the CDW superlattice. Interfacing 1T-NbSe₂ with metallic 2H-NbSe₂ provided a platform to investigate the competition between Heisenberg coupling of local moments and Kondo coupling in a two-dimensional system. STM measurements revealed high inhomogeneities of electronic structure on the nanometer scale. This inhomogeneities is due to the incommensurate stacking of √13×√13 CDW in 1T-NbSe₂ and √3×√3 CDW in 2H-NbSe₂.The second system of this thesis focuses on engineering flat bands through superlattice engineering. By stacking graphene on 1T-NbSe₂/2H-NbSe₂ with controlled twist angles, two near-commensurate superlattices—2×2 and √3×√3—aligned with the CDWof 1T-NbSe₂ were realized. In the 2×2 superlattice, the C₃ rotational symmetry was preserved, while in the √3×√3 superlattice, a stripe phase with C₂ rotational symmetry emerged, indicating broken symmetry and tunable electronic behaviours. The third part investigates flat bands in systems with highly anisotropic band structures, exemplified by the 2D magnet CrSBr. In CrSBr, weak interlayer coupling results in dispersive electronic states along one-dimensional chains, but localized with the chains. By engineering CrSBr on 2H-NbSe₂, STM visualized the quasi-one-dimensional electronic structure in real space with high spatial and energy resolution. Furthermore, a reconstruction of the electronic band structure of CrSBr induced by spin canting in the external magnetic field was observed. This work provides fundamental insight into the interplay between electronic structure, symmetry breaking, and magnetic ordering in van der Waals heterostructures and presents a key step for future research on the emergence and manipulation of quantum phenomena in these systems. LB - PUB:(DE-HGF)11 DO - DOI:10.18154/RWTH-2025-10153 UR - https://publications.rwth-aachen.de/record/1022651 ER -