Giant and tunable Rashba spin splitting and quantum spin Hall effect in H-Pb-Cl

Abstract

Rashba spin splitting and quantum spin Hall effect have attracted enormous interest due to their great significance in the application of spintronics. Based on the first-principles calculation, we propose a two-dimensional hexagonal lattice material H-Pb-Cl, which realizes the coexistence of giant Rashba spin splitting and quantum spin Hall effect. Due to the breaking of space inversion symmetry and the existence of intrinsic electric field, H-Pb-Cl has a huge Rashba spin splitting phenomenon (α<sub>R</sub>=3.78eVÅ), and the Rashba spin splitting of H-Pb-Cl(-16%-16%) can be adjusted with the change of biaxial stress. By analyzing the electronic properties of H-Pb-Cl, we find that H-Pb-Cl has a huge band gap near the Fermi surface (1.31eV), and the topological invariant Z<sub>2</sub>=1 of the system is caused by the inversion of s-p orbit, which indicates that H-Pb-Cl is a two-dimensional topological insulator with a huge topological band gap, and the gap is large enough for the observation of topological edge states at room temperature. In addition, we further consider the effect of BN and graphane substrates on the topological band gap of H-Pb-Cl by using the H-Pb- Cl (111)-(1×1) /BN (111)-(2×2) and H-Pb-Cl(1×1)/ graphane (2×2) system, and find the lattice mismatch between H-Pb-Cl (5.395 Å) and BN (2.615 Å) and graphane（2.575 Å）are about 3% and 4.5%, respectively. According to our calculation results, H-Pb-Cl still retains the properties of topological insulator under the effect of spin orbit coupling, and is not affected by the BN and graphane. Our results show that the nontrivial topological band gap of H-Pb-Cl can be well preserved under both biaxial stress and substrate effects. In addition, because H-Pb-Cl can well retain the nontrivial topological band gap under the stress of -16% to 16%, and thus there are many kinds of substrate materials used for the synthesis of this material, which is very helpful for the successful preparation of experiments. Our research provides a promising candidate material for exploring and realizing the coexistence of Rashba spin splitting and quantum spin Hall effect. And the coexistence of giant Rashba spin splitting and quantum spin Hall effect greatly broadens the potential application of H-Pb-Cl in the field of spintronic devices.