Sublattice dependence and gate-tunability of midgap and resonant states induced by native dopants in Bernal-stacked bilayer graphene

TL;DR

This study confirms the existence of dopant-induced midgap and resonant states in Bernal-stacked bilayer graphene, demonstrating their sublattice dependence and gate-tunability, which influence the material's electronic properties.

Contribution

It provides experimental evidence and theoretical support for dopant-induced midgap states in bilayer graphene, highlighting their sublattice-specific behavior and tunability.

Findings

Midgap states appear when dopants are on non-dimer sublattice sites.

Narrow resonances occur at high energy band edges for dopants on dimer sites.

Gate-tunability of midgap states enables control over electronic properties.

Abstract

The properties of semiconductors can be crucially impacted by midgap states induced by dopants, which can be native or intentionally incorporated in the crystal lattice. For Bernal-stacked bilayer graphene (BLG), which has a tunable bandgap, the existence of midgap states induced by dopants has been conjectured, but never confirmed experimentally. Here, we report scanning tunneling microscopy and spectroscopy results, supported by tight-binding calculations, that demonstrate the existence of midgap states in BLG. We show that the midgap state in BLG -- for which we demonstrate gate-tunability -- appears when the dopant is hosted on the non-dimer sublattice sites. We further evidence the presence of narrow resonances at the onset of the high energy bands (valence or conduction, depending on the dopant type) when the dopants lie on the dimer sublattice sites. These results suggest that dopants/defects can play an important role in the transport and optical properties of multilayer graphene samples, especially at energies close to the band extrema.