Abstract
Topological insulators host spin-polarized surface states born out of the energetic inversion of bulk bands driven by the spin-orbit interaction. Here we discover previously unidentified consequences of band-inversion on the surface electronic structure of the topological insulator Bi2Se3. By performing simultaneous spin, time, and angle-resolved photoemission spectroscopy, we map the spin-polarized unoccupied electronic structure and identify a surface resonance which is distinct from the topological surface state, yet shares a similar spin-orbital texture with opposite orientation. Its momentum dependence and spin texture imply an intimate connection with the topological surface state. Calculations show these two distinct states can emerge from trivial Rashba-like states that change topology through the spin-orbit-induced band inversion. This work thus provides a compelling view of the coevolution of surface states through a topological phase transition, enabled by the unique capability of directly measuring the spin-polarized unoccupied band structure.
Highlights
Topological insulators host spin-polarized surface states born out of the energetic inversion of bulk bands driven by the spin-orbit interaction
Our observation of the unoccupied surface resonance (USR) is corroborated by density functional theory (DFT) calculations, and tight-binding calculations provide plausible scenarios in which the spin textures of the USR and topological surface state (TSS) are intimately related as the two coevolve from a pair of Rashba-like states through the spin-orbit interaction (SOI) band inversion
We find that the addition of a phenomenological term to the Hamiltonian of the standard surface Rashba form qualitatively reproduces the USR: a spin-polarized surface-localized state split above the bulk conduction band (BCB), with the USR’s characteristic reduction in strength towards G and its spin-polarization oriented opposite to that of the TSS as shown on the far left of Fig. 5
Summary
Topological insulators host spin-polarized surface states born out of the energetic inversion of bulk bands driven by the spin-orbit interaction. The remarkable progress of theoretical and experimental studies on topological insulators has dramatically deepened our understanding of how the spin-orbit interaction (SOI) can shape electronic bandstructure in solids It is well-established that band inversion driven by SOI is responsible for the formation of a topological surface state (TSS) in a range of materials[1,2,3,4]. We provide new insights on SOI-driven band inversion by employing spin, time, and angle-resolved photoemission spectroscopy (STARPES) to study the spin polarization of transiently occupied states above the Fermi energy, EF in the prototypical topological insulator Bi2Se3 through optical pump excitation. Our observation of the USR is corroborated by density functional theory (DFT) calculations, and tight-binding calculations provide plausible scenarios in which the spin textures of the USR and TSS are intimately related as the two coevolve from a pair of Rashba-like states through the SOI band inversion
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