In this PhD thesis, the recombination of different atomic lattices in stacked 2D materials such as twisted bilayer graphene is studied. Using the different possibilities of Low-Energy Electron... Show moreIn this PhD thesis, the recombination of different atomic lattices in stacked 2D materials such as twisted bilayer graphene is studied. Using the different possibilities of Low-Energy Electron Microscopy (LEEM), the domain forming between the two atomic layers with small differences is studied. Superlattices in three such 2D material systems are studied. In twisted bilayer graphene, the small difference is caused by a twist of approximately one degree between the layers. In graphene on SiC, the difference is caused by the lattice mismatch between a buffer layer bound to the substrate and the next graphene layer. For both, we show that domains of different shapes and sizes occur and relate them to strain and lattice mismatch. The third system studied is tantalum disulfide. In this layered material, two different superlattices occur: a superlattice between atomic layers with different atomic arrangements in the layers, so-called polytypes, and the superlattices between the atomic lattice and the Charge Density Waves (CDW). CDWs cause a large temperature dependent resistivity change. The influence of a mixture of different polytypes on the precise CDW states is studied using LEEM spectroscopy and local Low-Energy Electron Diffraction. Show less
Transport experiments in twisted bilayer graphene haverevealed multiple superconducting domes separated by cor-related insulating states 1–5 . These properties are generallyassociated with strongly... Show moreTransport experiments in twisted bilayer graphene haverevealed multiple superconducting domes separated by cor-related insulating states 1–5 . These properties are generallyassociated with strongly correlated states in a flat mini-bandof the hexagonal moiré superlattice as was predicted by bandstructure calculations 6–8 . Evidence for the existence of a flatband comes from local tunnelling spectroscopy 9–13 and elec-tronic compressibility measurements 14 , which report two ormore sharp peaks in the density of states that may be asso-ciated with closely spaced Van Hove singularities. However,direct momentum-resolved measurements have proved to bechallenging 15 . Here, we combine different imaging techniquesand angle-resolved photoemission with simultaneous real- andmomentum-space resolution (nano-ARPES) to directly mapthe band dispersion in twisted bilayer graphene devices nearcharge neutrality. Our experiments reveal large areas with ahomogeneous twist angle that support a flat band with a spec-tral weight that is highly localized in momentum space. The flatband is separated from the dispersive Dirac bands, which showmultiple moiré hybridization gaps. These data establish thesalient features of the twisted bilayer graphene band structure. Show less
