# Two-dimensional Weyl Half Semimetal and Tunable Quantum Anomalous Hall Effect in Monolayer PtCl$_{3}$

## TL;DR

This paper introduces the concept of a two-dimensional Weyl half semimetal state, predicts its realization in monolayer PtCl3, and demonstrates how its topological properties can be tuned via magnetization rotation for potential electronic applications.

## Contribution

It proposes a novel 2D Weyl half semimetal state, predicts its existence in monolayer PtCl3, and shows tunable topological phase transitions between quantum anomalous Hall states.

## Key findings

- Monolayer PtCl3 is a half metal with fully spin-polarized Weyl points.
- The Weyl points are protected by mirror symmetry and robust against spin-orbit coupling.
- Magnetization rotation can switch between quantum anomalous Hall phases.

## Abstract

We propose a new topological quantum state of matter---the two-dimensional (2D) Weyl half semimetal (WHS), which features 2D Weyl points at Fermi level belonging to a single spin channel, such that the low-energy electrons are described by fully spin-polarized 2D Weyl fermions. We predict its realization in the ground state of monolayer PtCl$_3$. We show that the material is a half metal with an in-plane magnetization, and its Fermi surface consists of a pair of fully spin-polarized Weyl points protected by a mirror symmetry, which are robust against spin-orbit coupling. Remarkably, we show that the WHS state is a critical state at the topological phase transition between two quantum anomalous Hall insulator phases with opposite Chern numbers, such that a switching between quantum anomalous Hall states can be readily achieved by rotating the magnetization direction. Our findings demonstrate that WHS offers new opportunity to control the chiral edge channels, which will be useful for designing new topological electronic devices.