Spin splitting and spin Hall conductivity in buckled monolayers of the group 14: First-principles calculations

TL;DR

This study uses first-principles calculations to analyze how electric fields affect spin splitting and spin Hall conductivity in buckled group 14 monolayers, revealing their potential for tunable spintronic applications.

Contribution

It provides a detailed first-principles analysis of electric field effects on spin-dependent properties in buckled group 14 monolayers, including spin Hall conductivity behavior.

Findings

Spin Hall conductivity is not quantized and degrades with electric field in silicene, germanene, and stanene.

Plumbene's spin Hall conductivity remains robust against electric field variations.

Electric field can invert the band gap, affecting topological phases in these materials.

Abstract

Elemental monolayers of the group 14 with a buckled honeycomb structure, namely silicene, germanene, stanene, and plumbene, are known to demonstrate a spin splitting as a result of an electric field parallel to their high symmetry axis which is capable of tuning their topological phase between a quantum spin Hall insulator and an ordinary band insulator. We perform first-principles calculations based on the density functional theory to quantify the spin-dependent band gaps and the spin splitting as a function of the applied electric field and extract the main coefficients of the invariant Hamiltonian. Using the linear response theory and the Wannier interpolation method, we calculate the spin Hall conductivity in the monolayers and study its sensitivity to an external electric field. Our results show that the spin Hall conductivity is not quantized and in the case of silicene, germanene, and stanene degrades significantly as the electric field inverts the band gap and brings the monolayer into the trivial phase. The electric field induced band gap does not close in the case of plumbene which shows a spin Hall conductivity that is robust to the external electric field.