Monolayer and bilayer PtCl$_3$: Energetics, magnetism, and band topology

TL;DR

This study explores the stability, magnetic properties, and topological phases of monolayer and bilayer PtCl3, revealing potential for realizing 2D Weyl half-semimetal, quantum anomalous Hall, and magnetic mirror Chern insulator states.

Contribution

It provides comprehensive theoretical analysis of 2D and bilayer PtCl3, identifying stable structures and topological phases, and suggests experimental pathways for realization.

Findings

PtCl3 is thermally stable up to 600 K.

Uniaxial strain can induce a topological phase transition.

AA' stacked bilayer exhibits a magnetic mirror Chern insulator state.

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 PtCl$_3$ was predicted as a platform for realizing this state. Here, we perform an extensive search of 2D PtCl$_3$ structures, by using the particle swarm optimization technique and density functional theory calculation. We show that the desired 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 SnS$_2$ as a substrate for the growth of 2D PtCl$_3$, which has excellent lattice matching and preserves the WHS state in 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 PtCl$_3$ and show that the stacking configuration has strong impact on the magnetism and the electronic band structure. Particularly, the $AA'$ stacked bilayer 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 PtCl$_3$ and will facilitate the study of 2D magnetic topological states, including WHS, QAH insulator, and magnetic mirror Chern insulator states.