Strain-tunable quantum anomalous Hall effect/quantum anomalous valley Hall effect in two-dimensional ferromagnetic non-Dirac topological half-metal N₂Pd₄S₆

Systems with both the quantum anomalous Hall (QAH) effect and the quantum anomalous valley Hall (QAVH) effect have wide appeal in fundamental research and practical quantum device applications. By using first-principles calculations, the topologically nontrivial phase and QAH effect were predicted in the ferromagnetic non-Dirac half-metal N₂Pd₄S₆ monolayer. The N₂Pd₄S₆ monolayer prefers out-of-plane magnetization and exhibits a Curie temperature of ∼80 K due to dual double-exchange interaction. Upon application of − 1% strain, the Curie temperature can reach up to ∼117 K. Furthermore, the N₂Pd₄S₆ monolayer exhibits a non-Dirac band dispersion near the Fermi level. The introduction of magnetic exchange and spin-orbit coupling (SOC) together enables to realize topologically nontrivial phase and QAH state. Remarkably, the compressive strain induces spontaneous valley polarization at the non-high symmetry point, thereby enabling the unique QAVH effect. Reversible switching between the QAH and QAVH effect can be achieved in the N₂Pd₄S₆ monolayer by applying of compression strain.