First-principles studies of Rashba effect on a two-dimensional topological insulator.

Finding giant Rashba effect materials is of great importance to realize new spin-driven devices. Using first-principles DFT calculations, we report a giant Rashba effect, and possibly switchable spin textures with external electric field found on one of two-dimensional topological insulators in group-11 chalcogenide compounds. The stable structure of this material is polar with broken inversion symmetry along c axis with calculated dipole moment of 5.1 pC/m. The strong spin-orbit coupling responsible for the band inversion is calculated to be about 130 meV, which is significantly larger than other widely celebrated topological insulators. The calculated band structure shows a giant Rashba type spin splitting in the valence band. The Rashba coefficient is about 3.7 eVÅ, comparable with that of the bulk Rashba material BiTeI. We also present the switchable energy barrier (~0.1eV/f.u.) between the two polar states, and accordingly spin texture changes, providing an effective way to control the magnetic structure using external electric fields.