Electronic Structure Modeling for 2D Layered Material Stacks
With the development of the experimental techniques to synthesize and characterize the two-dimensional van der Waals layered materials, more layer types are discovered and studied which include examples of graphene, hexagonal boron-nitride and various transition metal dichalcogenides crystals. These layers host a variety of physical properties such as charge density waves, superconductivity, magnetism, topological phases, and more. The layer geometry allows various heterostructures to be fabricated and tuning of the band structure properties. These would have implications on fundamental physics research and potential device applications. However, it also poses great challenges to the theoretical simulations when considering the modeling of various layer types, the strain effects within the layers, the stacking order between layers and the rotation angle in between. These could have dramatic effects on the electronic structure under the right conditions. For example, when the twisted bilayer graphene are rotated at the “magic angle” about one degree, the flat bands emerge from the hybridization of Dirac electrons and give rise to the superconducting states and correlated Mott phases. I will discuss the numerical multi-scale approach to the simulation of the van der Waals layers and their heterostructures. The efficient tight-binding Hamiltonians are constructed based on the Wannier transformations of the density functional theory calculations, which also enable us to derive the interlayer coupling terms relevant to the simulations of the twisted layers stacks with the given layer types.
This work was supported by the STC Center for Integrated Quantum Materials, NSF Grant No. DMR-1231319 and by ARO MURI Award W911NF-14-0247.