The dual topological phases in X₃AsTe₄ (X = Zr, Hf) monolayers

The quantum anomalous Hall effect (QAHE) and the quantum spin Hall effect (QSHE) hold great potential for advancing next-generation low-power, high-ruggedness electronic and quantum devices. Here, using first-principles calculations, we investigate the interplay between magnetic order and band topology in the two-dimensional (2D) semimetal system X₃AsTe₄ (X = Zr, Hf). We find that X₃AsTe₄ (X = Zr, Hf) is a promising material exhibiting ferromagnetic (FM) properties. The highly hybridized electronic orbitals near the Fermi level give rise to strong electronic correlations, leading to the formation of intriguing non-Dirac bands and rendering X₃AsTe₄ (X = Zr, Hf) a 2D semimetal. Upon including spin-orbit coupling (SOC), a QAH gap opens at the Fermi level. Within this QAH gap, two chiral edge states with the same propagation direction emerge, demonstrating that X₃AsTe₄ (X = Zr, Hf) is an ideal platform for realizing a high-Chern-number QAHE with C = 2. Meanwhile, X₃AsTe₄ (X = Zr, Hf) hosts a QSH gap at an energy of approximately 0.45 eV above the Fermi level, making X₃AsTe₄ (X = Zr, Hf) a dual-topological-phase material hosting both a high-Chern-number QAH state and a QSH state. Furthermore, we find that applying biaxial strain to X₃AsTe₄ (X = Zr, Hf) enables the tuning of the material's metallicity and the switching of its easy magnetization axis, and a slight biaxial tensile strain can effectively enlarge the QSH gap of monolayer Hf₃AsTe₄, thereby enhancing the stability of its QSHE. Our study greatly enriches the research on dual-topological-phase materials and provides a powerful route toward the realization of novel quantum devices.