Structure-driven intercalated architecture of septuple-atomic-layer $MA_2Z_4$ family with diverse properties from semiconductor to topological insulator to Ising superconductor

TL;DR

This paper introduces a new family of septuple-atomic-layer $MA_2Z_4$ monolayers with diverse electronic properties, constructed via a general intercalation approach, predicting 66 stable materials with potential applications from semiconductors to topological insulators.

Contribution

The paper develops a general method to construct and predict a large family of stable $MA_2Z_4$ monolayers with diverse properties, including the synthesis of known materials and prediction of new stable compounds.

Findings

Reproduced experimentally synthesized $MA_2Z_4$ monolayers.

Predicted 66 new thermodynamically stable $MA_2Z_4$ monolayers.

Identified specific $MA_2Z_4$ materials with potential for spin-valley polarization, superconductivity, and topological insulating behavior.

Abstract

Motivated by the fact that septuple-atomic-layer MnBi$_2$Te$_4$ can be structurally viewed as the combination of double-atomic-layer MnTe intercalating into quintuple-atomic-layer Bi$_2$Te$_3$, we present a general approach of constructing twelve septuple-atomic-layer $\alpha_i$- and $\beta_i$-$MA_2Z_4$ monolayer family (\emph{i} = 1 to 6) by intercalating MoS$_2$-type $MZ$$_2$ monolayer into InSe-type A$_2$Z$_2$ monolayer. Besides reproducing the experimentally synthesized $\alpha_1$-MoSi$_2$N$_4$, $\alpha_1$-WSi$_2$N$_4$ and $\beta_5$-MnBi$_2$Te$_4$ monolayer materials, another 66 thermodynamically and dynamically stable $MA_2Z_4$ were predicted, which span a wide range of properties upon the number of valence electrons (VEC). $MA_2Z_4$ with the rules of 32 or 34 VEC are mostly semiconductors with direct or indirect band gap and, however, with 33 VEC are generally metal, half-metal ferromagnetism, or spin-gapless semiconductor upon whether or not an unpaired electron is spin polarized. Moreover, we propose $\alpha_2$-WSi$_2$P$_4$ for the spin-valley polarization, $\alpha_1$-TaSi$_2$N$_4$ for Ising superconductor and $\beta_2$-SrGa$_2$Se$_4$ for topological insulator.