Quantum Spin Hall Effect in Silicene

TL;DR

This paper demonstrates that silicene exhibits a quantum spin Hall effect due to its topologically nontrivial electronic structure, with a sizable spin-orbit gap making it promising for low-temperature spintronics applications.

Contribution

The study provides first-principles evidence of QSHE in silicene, including calculations of the Z2 invariant and effects of strain, highlighting its potential for spintronics.

Findings

Silicene has a spin-orbit gap of 1.55 meV, observable at low temperatures.

Applying pressure increases the gap to 2.90 meV.

Germanium with similar structure shows a SOC gap of 23.9 meV.

Abstract

Recent years have witnessed great interest in the quantum spin Hall effect (QSHE) which is a new quantum state of matter with nontrivial topological property due to the scientific importance as a novel quantum state and the technological applications in spintronics. Taking account of Si, Ge significant importance as semiconductor material and intense interest in the realization of QSHE for spintronics, here we investigate the spin-orbit opened energy gap and the band topology in recently synthesized silicene using first-principles calculations. We demonstrate that silicene with topologically nontrivial electronic structures can realize QSHE by exploiting adiabatic continuity and direct calculation of the Z2 topological invariant. We predict that QSHE in silicene can be observed in an experimentally accessible low temperature regime with the spin-orbit band gap of 1.55 meV, much higher than that of graphene due to large spin-orbit coupling and the low-buckled structure. Furthermore, we find that the gap will increase to 2.90 meV under certain pressure strain. Finally, we also study germanium with similar low buckled stable structure, and predict that SOC opens a band gap of 23.9 meV, much higher than the liquid nitrogen temperature.