Twisted-bilayer FeSe and the Fe-based superlattices

We derive BM-like continuum models for the bands of superlattice heterostructures formed out of Fe-chalcogenide monolayers: (I) a single monolayer experiencing an external periodic potential, and (II) twisted bilayers with long-range moire tunneling. A symmetry derivation for the inter-layer moire tunnelling is provided for both the Γ and M high-symmetry points. In this paper, we focus on moire bands formed from hole-band maxima centered on Γ, and show the possibility of moire bands with C = 0 or ±1 topological quantum numbers without breaking time-reversal symmetry. In the C = 0 region for θ → 0 (and similarly in the limit of large superlattice period for I), the system becomes a square lattice of 2D harmonic oscillators. We fit our model to FeSe and argue that it is a viable platform for the simulation of the square Hubbard model with tunable interaction strength.