Large Gap Topological Insulating Phase and Anisotropic Rashba and Chiral Spin Textures in Monolayer Zintl A₂MX₂

Abstract

A family of two-dimensional (2D) materials, particularly the complex-structured Zintl phase compounds, has attracted tremendous research attention because of tunable material properties and exceptional applications. Utilizing first-principles computations under the hybrid functional approach, we performed a systematic study on A2MX2 (A = Ca, Sr, or Yb; M = Zn or Cd; X = P, As, Sb, or Bi). Among the three surface terminations considered, the metal element XM-termination (T2) was found to be the most stable structural phase with the lowest total ground state energies. Thermodynamic stability was further confirmed through phonon dispersion and formation energy calculations. Surprisingly, the T2 monolayer Sr2CdBi2 was found to host the topological insulating phase with a sizable bandgap of 556 meV, as well as a Z2 topological invariance of 1. The corresponding topologically protected edge states link the conduction and valence bands. Moreover, the topological phase is driven by the spin–orbit coupling, which causes the inverted bands at Γ point close to the Fermi level concerning the Cd- s + Bi2- s and Bi2- px + py orbitals. Moreover, Rashba and chiral spin-splittings were also observed. The computed Rashba strengths along Γ-M (αR Γ‑M) are 1.970, 0.676, and 0.669 eV·Å, whereas the computed values along Γ-K (αR Γ‑K) are 1.701, 0.731, and 0.646 eV·Å, for Ca2ZnAs2, Sr2CdBi2, and Yb2ZnAs2, respectively. Our study provides fundamental knowledge to further experimental investigations and synthesis, which may lead to electronic applications of A2MX2 compounds in quantum computing or spintronics.

Exploiting the fraternal twin nature of thermoelectrics and topological insulators in Zintl phases as a tool for engineering new efficient thermoelectric generators

“…[70][71][72][73][74][75][76] Besides the exploration of the Zintl phase materials for TE applications, an increasingly growing trend is the observation of topological properties of matter in a number of these phases. [77][78][79][80] Several excellent TE materials are known to possess nontrivial topological properties as it appears both favor the same material properties such as strong spin orbit coupling (SOC) and narrow band gap. 46,81,82 Furthermore, it is known that several topological materials also exhibit some form of enhanced TE properties as strong correlations exist between the surface state properties of a topological material and transport properties such as S, s and others, such that an enhanced TE performance can be achieved by tuning the surface properties.…”

Obtaining giant Rashba–Dresselhaus spin splitting in two-dimensional chiral metal–organic frameworks

“…13,14 Despite the great potential of the R-D effect, achieving giant spin splitting in 2D materials is limited to a few inorganic semiconductors. [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] Moreover, the underlying factors inuencing spin splitting and the general method to achieve giant spin splitting remain to be explored.…”