Lattice Expansion Leads to the Renormalization of Bulk-State Valence Band Structure and Band Gap in Bi₂Se₃

The continuous conduction band can be tuned to several Rashba spin-splitting quantum wells in the bulk states of layered Bi₂Se₃ via alkali metal evaporation. However, the corresponding bulk-state valence band structure and band gap evolution have not been studied in depth yet. Here, we systematically investigate the electronic band structures of Bi₂Se₃ upon in situ K atom deposition via angle-resolved photoelectron spectroscopy (ARPES). The valence band renormalizes in both energy and momentum space, and the band gap reduces from 450 to 400 meV. Alkali metal deposition results in electron doping and interfacial dipole electric field, which are two major factors modulating the electronic structures of materials. Expanding the lattice of Bi₂Se₃, our density functional theory (DFT) calculations qualitatively reproduce the experimentally detected evolution of the valence band structure and the band gap value, through either electron doping or manual setting. However, neither electron injection nor the interfacial dipole electric field alone induces such an evolution when the lattice of Bi₂Se₃ is fixed. This finding indicates that lattice expansion induced by potassium deposition at the Bi₂Se₃ surface exerts a significant influence on the bulk electronic band structure, a result that will facilitate the manipulation of the electronic structure and applications of this material.