Description
Moiré superlattices — the long-wavelength patterns that emerge when atomically thin crystals are stacked with a small twist or lattice mismatch — have become a versatile means of reshaping the electronic structure of two-dimensional materials. Yet the physics accessible in these systems is largely dictated by the geometries of the constituent crystals, restricting the design space to what stacking allows.
Here, we show that a self-assembled molecular overlayer can act as an independent superlattice potential on graphene. We fabricate a graphene/hexagonal boron nitride (hBN) heterostructure and deposit an ordered layer of organic molecules on top, producing two coexisting moiré superlattice perturbations: one from the hBN substrate below, one from the molecular layer above.
Using low-temperature, gate-dependent scanning tunnelling spectroscopy, we compare the graphene/hBN electronic structure before and after molecular self-assembly. The molecular layer leaves graphene’s primary Dirac point essentially unchanged, indicating little net charge transfer, but shifts electronic states associated with the graphene/hBN superlattice by approximately 70 meV towards charge neutrality.
To interpret these observations, we develop a two-potential continuum model incorporating both the hBN and molecular superlattices. The molecular contribution is consistent with a predominantly scalar moiré potential with a characteristic strength of 200–250 meV, around twenty times larger than the scalar component associated with hBN. Our results establish molecular self-assembly as a flexible complement to twist-angle engineering and open a route towards chemistry-tuneable moiré superlattices.
| I am the presenting author | Yes |
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