Quantum Spin Hall Effect in Ta$_2$M$_3$Te$_5$ (M = Pd, Ni)

TL;DR

This paper predicts that monolayer Ta2Pd3Te5 is a quantum spin Hall insulator with tunable properties, based on first-principles calculations, highlighting its potential for spintronics and quantum computing applications.

Contribution

The study demonstrates the QSH effect in monolayer Ta2Pd3Te5 through first-principles calculations, revealing its topological properties and strain-tunability, which is a novel prediction for this material.

Findings

Monolayer Ta2Pd3Te5 is a QSH insulator with a nontrivial topology.

Spin-orbit coupling opens a global gap, enabling the QSH state.

QSH state can be tuned by external strain.

Abstract

Quantum spin Hall (QSH) effect with great promise for the potential application in spintronics and quantum computing has attracted extensive research interest from both theoretical and experimental researchers. Here, we predict monolayer Ta$_2$Pd$_3$Te$_5$ can be a QSH insulator based on first-principles calculations. The interlayer binding energy in the layered van der Waals compound Ta$_2$Pd$_3$Te$_5$ is 19.6 meV/A$^2$; thus, its monolayer/thin-film structures could be readily obtained by exfoliation. The band inversion near the Fermi level ($E_F$) is an intrinsic characteristic, which happens between Ta-$5d$ and Pd-$4d$ orbitals without spin-orbit coupling (SOC). The SOC effect opens a global gap and makes the system a QSH insulator. With the $d$-$d$ band-inverted feature, the nontrivial topology in monolayer Ta$_2$Pd$_3$Te$_5$ is characterized by the time-reversal topological invariant $\mathbb Z_2=1$, which is computed by the one-dimensional (1D) Wilson loop method as implemented in our first-principles calculations. The helical edge modes are also obtained using surface Green's function method. Our calculations show that the QSH state in Ta$_2M_3$Te$_5$ ($M=$ Pd, Ni) can be tuned by external strain. These monolayers and thin films provide feasible platforms for realizing QSH effect as well as related devices.