Abstract:
The incommensurate stacking of multilayered two-dimensional materials is a challenging problem from a theoretical perspective and an intriguing avenue for manipulating their physical properties. The configuration (disregistry) space is a natural description of such incommensurate layered materials, based on the local environment of atomic positions and gives an exact formulation of the electronic properties such as the density of states and Kubo optical conductivity for an incommensurate structure. Our configuration space approach can also model heterostructures such as twisted trilayer graphene for which there does not exist a 2D moiré superlattice by reformulating the moiré of moiré structure in the 4D configuration space.
The Bistritzer-MacDonald (BM) model attempts to capture the electronic properties of twisted bilayer graphene (TBG) by an effective periodic model over the bilayer moiré pattern in the low energy, continuum limit. Starting from a tight-binding model, we identify a regime where the BM model emerges as the effective dynamics for electrons modeled as wave-packets spectrally concentrated at the monolayer Dirac points, up to error that we rigorously estimate. Using measured values of relevant physical constants, we argue that this regime is realized in TBG at the first “magic" angle.
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Lunch will be provided at 12:00pm, so please come early to eat mingle and eat lunch before the talk begins.