Surface Doped α-Bismuthene Studied by Angle-resolved Photoemission Spectroscopy

We investigated surface electron doping effects in ultrathin α-bismuthene (α-Bi) films on trilayer graphene using angle-resolved photoemission spectroscopy. Potassium adsorption induces an almost rigid downward shift of the band structure in both one-bilayer (1-BL) and two-bilayer (2-BL) films. In 2-BL α-Bi, this shift results in the occupation of an electron pocket along the Γ–X1 direction while preserving a finite band gap. In contrast, 1-BL α-Bi exhibits a vanishing of the observable band gap without populating the expected electron pocket. This profound alteration can be attributed to the highly asymmetric environment bounded by the substrate and K adatoms, which generates a strong perpendicular electric field that counteracts the spin-orbit-induced energy gap.