Monolayer and bilayer PtCl3 : Energetics, magnetism, and band topology

Abstract

Two-dimensional (2D) magnetic materials hosting nontrivial topological states are interesting for fundamental research as well as practical applications. Recently, the topological state of 2D Weyl half-semimetal (WHS) was proposed, which hosts fully spin polarized Weyl points robust against spin-orbit coupling in a 2D ferromagnetic system, and single-layer ${\mathrm{PtCl}}_{3}$ was predicted as a platform for realizing this state. Here, we perform an extensive search of 2D ${\mathrm{PtCl}}_{3}$ structures, by using the particle swarm optimization technique and density-functional theory calculation. We show that the desired ${\mathrm{PtCl}}_{3}$ phase corresponds to the most stable one at its stoichiometry. The 2D structure also possesses good thermal stability up to 600 K. We suggest ${\mathrm{SnS}}_{2}$ as a substrate for the growth of 2D ${\mathrm{PtCl}}_{3}$, which has excellent lattice matching and preserves the WHS state in ${\mathrm{PtCl}}_{3}$. We find that uniaxial strains along the zigzag direction maintain the WHS state, whereas small strains along the armchair direction drives a topological phase transition from the WHS to a quantum anomalous Hall (QAH) insulator phase. Furthermore, we study bilayer ${\mathrm{PtCl}}_{3}$ and show that the stacking configuration has strong impact on the magnetism and the electronic band structure. Particularly, the $A{A}^{\ensuremath{'}}$ stacked bilayer ${\mathrm{PtCl}}_{3}$ realizes an interesting topological state---the 2D antiferromagnetic mirror Chern insulator, which has a pair of topological gapless edge bands. Our work provides guidance for the experimental realization of 2D ${\mathrm{PtCl}}_{3}$ and will facilitate the study of 2D magnetic topological states, including WHS, QAH insulator, and magnetic mirror Chern insulator states.