Precision in Two Dimensions: Analysis of Topological Quantum Materials

New Topological Insulators (TI) quantum materials with fascinating properties promises to transform device design particularly with the ability to make stacked pseudo two-dimensional heterointerfaces. Some of the quantum phenomena displayed by these materials now persists at room temperature, Ba₆Nb₁₁S₂₈ naturally realizes vdW coupled heterointerfaces between transition metal dichalcogenide (TMD) monolayers (hexagonal NbS₂, H-NbS₂) and insulating spacers Ba₃NbS₅. Low Energy Electron Diffraction (LEED) taken along the c-axis shows that the hexagonal spacer and TMD layers, are commensurate. The electronic band structure can be understood as that resulting from superimposing a periodic potential defined by Ba₃NbS₅ onto monolayer H-NbS₂. This mechanism which yields flat energy bands and correlated physics in twisted-bilayer graphene and TMD heterostructures and is one of the key advances in the corelation of band structure and properties. We have shown with STEM, L/PEEM methods that new approaches are needed to identify the sub-structures of complex material. LEEM is a low- energy electron probe method that allows fine surface probing down to several layers. We show that new approaches to probing methods can show that behaviour is a consequence of the underlying symmetry properties of the multi-layer system.