Large Band Gap in a Quantum Spin Hall Insulator with Weak Spin-Orbit Coupling

The typical quantum spin Hall (QSH) insulator acquires its band gap through spin-orbit coupling (SOC). However, the intrinsic SOC in most materials is rather weak and creates small band gaps comparable to k(B)T. Here, we present a method to open a giant band gap (>1eV) in a QSH phase with a weak SOC, employing the tight-binding (TB) Kane-Mele model for the QSH insulator with the additional feature of periodic defects. By tuning the periodicity of structural defects, one can induce the intervalley scattering to open a large band gap, and we show that the characteristic metallic edge modes of a QSH phase persist even with the inclusion of such periodic defects. Our TB calculations show the existence of a Z(2) odd QSH phase in a Kane-Mele model modified to include periodic defects, demonstrating the coexistence of a giant band gap and the QSH effect with weak SOC.