Two-dimensional topological insulators of Pb/Sb honeycombs on a Ge(111) semiconductor surface

Based on first-principles hybrid functional calculations, we demonstrate the formation of two-dimensional (2D) topological insulators (TIs) of Pb/Sb honeycombs on Ge(111) semiconductor surface. We show that 1/3 Cl-covered Ge(111) surface offers an ideal template for metal deposition. When Pb and Sb atoms are deposited on Cl-Ge(111) surface, they spontaneously form a hexagonal lattice (Pb/Sb@Cl-Ge(111)). The Pb/Sb@Cl-Ge(111) exhibits a 2D TI state with large bulk gap of 0.27 eV for Pb@Cl-Ge(111) and 0.81 eV for Sb@Cl-Ge(111). The mechanism of 2D TI state is the substrate orbital-filtering effect that effectively removes the p bands of Pb(Sb) away from the Fermi level, leaving behind only the p and p orbitals at the Fermi level. Our findings pave another way for future design of 2D topological insulators on conventional semiconductor surface, which promotes the application of 2D TIs in spintronics and quantum computing devices at room-temperature.