Tailoring Robust Quantum Anomalous Hall Effect via Entropy‐Engineering

Abstract The development of quantum materials and the tailoring of their functional properties is of fundamental interest in materials science. Here, a new design concept is proposed for the robust quantum anomalous Hall (QAH) effect via entropy engineering in 2D magnets. As a prototypical example, the configurational entropy of monolayer transition metal trihalide VCl 3 is manipulated by incorporating four different transition‐metal cations [Ti,Cr,Fe,Co] into the honeycomb structure made of vanadium, such that all in‐plane mirror symmetries, inversion and/or roto‐inversion are broken. Monolayer VCl 3 is a ferromagnetic Dirac half‐metal in which spin‐polarized Dirac dispersion at valley momenta is accompanied by bulk states at the Γ‐point and thus the spin‐orbit interaction‐driven QAH phase does not exhibit fully gapped bulk band dispersion. Entropy‐driven bandstructure renormalization, especially band flattening in combination with red‐ and blue‐shifts at different momenta of the Brillouin zone and crystal‐field effects, transforms Dirac half‐metal to a Dirac spin‐gapless semiconductor and leads to a robust QAH phase with fully gapped bulk band dispersion and, thus, a purely topological edge state transport without mixing with dissipative bulk channels. These findings provide a paradigm for designing entropy‐engineered 2D materials for the realization of robust QAH effect and quantum device applications.