Formation of quantum spin Hall state on Si surface and energy gap scaling with strength of spin orbit coupling

摘要

For potential applications in spintronics and quantum computing, it isdesirable to place a quantum spin Hall insulator [i.e., a 2D topologicalinsulator (TI)] on a substrate while maintaining a large energy gap. Here, wedemonstrate a unique approach to create the large-gap 2D TI state on asemiconductor surface, based on first-principles calculations and effectiveHamiltonian analysis. We show that when heavy elements with strong spin orbitcoupling (SOC) such as Bi and Pb atoms are deposited on a patterned H-Si(111)surface into a hexagonal lattice, they exhibit a 2D TI state with a largeenergy gap of over 0.5 eV. The TI state arises from an intriguing substrateorbital filtering effect that selects a suitable orbital composition around theFermi level, so that the system can be matched onto a four-band effective modelHamiltonian. Furthermore, it is found that within this model, the SOC gap doesnot increase monotonically with the increasing strength of SOC. Theseinteresting results may shed new light in future design and fabrication oflarge-gap topological quantum states.