Twisted bilayer FeSe and Fe-based superlattices
Paul Myles Eugenio
Abstract: Emergent patterns formed from the overlap of 2D crystalline sheets induce a superlattice which can be used to tune the electronic order. Such moiré devices have become the platform for the simulation of model fermionic systems in condensed matter. The quintessential example being twisted bilayer graphene, which exhibits twist-angle and electron-filling-dependent strong-coupling insulation, pseudomagnetic fields, and superconductivity -- all possible to probe on the same device in situ.
We propose a family of such devices composed of twisted bilayers of monolayer FeSe, an iron-based superconductor. More precisely, we derive all possible moiré invariants in the low-energy continuum theory of FeSe; and show by fitting the bands at to photoemission and DFT, that twisted bilayers of FeSe have all the ingredients needed to simulate the square Hubbard model, the two-orbital Hubbard model, and higher in the small angle limit. We additionally map out a phase diagram as a function of the twist angle, and show a possible angle-dependent topological transition into a spin Hall phase.