Visualizing the conduction band and moiré effects in WS₂/WSe₂ heterobilayer devices by micro-ARPES

We investigate heterobilayers of WS₂ and WSe₂ aligned close to zero degrees, in which moiré superlattice effects are anticipated, using micron-scale-angle-resolved photoemission spectroscopy (micro-ARPES). The bilayer is partially capped by graphene and supported by a hexagonal boron nitride on graphite back gate in a field-effect transistor geometry. By applying a voltage to the back gate, we can electrostatically populate­ the heterobilayer conduction band minimum in the uncapped regions, finding that the conduction band edge is at the K-point in the WS₂ as anticipated. We also see other spectral features resembling the conduction band edge but displaced in momentum by reciprocal lattice vectors corresponding to the expected heterobilayer moiré lattice. In the graphene-capped regions, we observe replicas of the graphene bands displaced by similar vectors. The particular symmetry in photoemission intensity of these replicas, combined with the absence of replicas displaced by graphene/WS₂ or graphene/WSe₂ moiré vectors, provide indications that the replicas are band structure alterations due to the moiré modulation rather than copies of the unperturbed bands produced by final-state diffraction. Differentiating between these two possible origins of the additional spectral features however remains challenging.