Two-dimensional Weyl half-semimetal and tunable quantum anomalous Hall effect

A Weyl point is topologically stable in three dimensions, but is typically vulnerable in two dimensions of space, especially when spin-orbit coupling (SOC) and magnetic ordering are considered. Here, the authors predict a state, labeled as a Weyl half-semimetal, which hosts a stable magnetic Weyl point in two dimensions in the presence of SOC. It is simultaneously a Weyl semimetal and a half metal, such that the low-energy electrons are fully spin-polarized two-dimensional Weyl fermions. A specific material, the monolayer PtCl₃, is proposed to realize this state.