Large-gap quantum spin Hall state in functionalized dumbbell stanene

TL;DR

This paper predicts that methyl-functionalized dumbbell stanene exhibits a large bulk band gap and robust quantum spin Hall effect, tunable by strain and edge modifications, with potential applications in spintronics.

Contribution

The study demonstrates that methyl-functionalization significantly enhances the band gap of dumbbell stanene, enabling room-temperature QSHE and provides insights into substrate effects for device integration.

Findings

Band gap increased to 148 meV with methyl-functionalization

QSHE confirmed by band inversion and topological invariant

Edge states can be modulated by edge modifications

Abstract

Two-dimensional dumbbell (DB) stanene has been proposed as a promising candidate material for realizing quantum spin Hall effect (QSHE) by Tang et al [P. Tang, P. Chen, W. Cao, H. Huang, S. Cahangirov, L. Xian, Y. Xu, S. C. Zhang, W. Duan, A. Rubio. Phys. Rev. B, 90, 121408 (2014)]. However, the small bulk-gap limits its possible applications at room temperature. Based on first-principles calculations, we predict that its band gap can be enhanced to 148 meV under methyl-functionalization, which can be further tuned by applying lattice strain. The QSHE is confirmed by s-px,y band inversion, topological invariant Z2 = 1, and helical gapless edge within bulk band gap. Notably, the characteristic properties of edge states, such as the large Fermi velocity and Dirac cone, can be modulated by edge modification. The effects of substrates on topological properties are explored when it is grown on various substrates, like SiC, h-BN, and Bi2Te3 sheets. These findings provide significant guidance for future fabrication and realistic applications of QSHE based on stanene in spintronics.