Abstract
Moiré superlattices of van der Waals heterostructures provide a powerful way to engineer electronic structures of two-dimensional materials. Many novel quantum phenomena have emerged in graphene and transition metal dichalcogenide moiré systems. Twisted phosphorene offers another attractive system to explore moiré physics because phosphorene features an anisotropic rectangular lattice, different from isotropic hexagonal lattices previously reported. Here we report emerging anisotropic moiré optical transitions in twisted monolayer/bilayer phosphorenes. The optical resonances in phosphorene moiré superlattice depend sensitively on twist angle and are completely different from those in the constitute monolayer and bilayer phosphorene even for a twist angle as large as 19°. Our calculations reveal that the Γ-point direct bandgap and the rectangular lattice of phosphorene give rise to the remarkably strong moiré physics in large-twist-angle phosphorene heterostructures. This work highlights fresh opportunities to explore moiré physics in phosphorene and other van der Waals heterostructures with different lattice configurations.
Highlights
Moiré superlattices of van der Waals heterostructures provide a powerful way to engineer electronic structures of two-dimensional materials
Few-layer phosphorene samples were first mechanically exfoliated onto the surface of polydimethylsiloxane (PDMS) thin films, and transferred to 285nm thick silicon dioxide/silicon (SiO2/Si) substrates[25,26]
The very different conduction band minimum (CBM) and valence band maximum (VBM) coupling between the monolayer and bilayer phosphorene in the twisted heterostructure originates from the different electron Bloch wavefunctions at the CBM and VBM, as illustrated schematically in Figs. 4e and f, respectively
Summary
Moiré superlattices of van der Waals heterostructures provide a powerful way to engineer electronic structures of two-dimensional materials. Moiré superlattices, while moiré excitons have been reported in small-twist-angle transition metal dichalcogenide (TMDC) heterostructures, e.g., WS2/WSe29, MoSe2/WS210, and MoSe2/WSe2 heterostructures[11,12] All these materials (graphene, hBN, and TMDCs) belong to the 2D hexagonal structures with the electronic bandgap lying at the vertices (K and K′ points) of the Brillouin zone[13,14,15,16,17], and prominent moiré superlattice effects have been observed in small-twist-angle (θ < 2°) heterostructures[1,3,9,10,11,12,18]. We demonstrate the moiré potential completely changes the electronic band structure and gives rise to a new set of optical transitions in twisted monolayer/bilayer phosphorene heterostructure even for twist angles larger than 19°. The calculated optical responses of the monolayer/bilayer moiré superlattice agree well with our experimental observations
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