Tunable Electronic Properties of Janus MXene CrScCO ₂ : From Semiconductor to Spin‐Gapless Semiconductor via External Fields

The electronic structure, magnetic properties, and external‐field modulation behavior of the Janus MXene CrScCO 2 aresystematically studied via density functional theory (DFT + U ) and HSE06 calculations. Hubbard U parameters are set to U Cr = 3.5 eV and U Sc = 0 eV based on systematic tests of their effects on electronic and magnetic properties. At equilibrium, DFT+ U calculations suggest a nearly gapless state (approximately 0.016 eV). In contrast, the more accurate hybrid functional HSE06 yields a small but finite band gap of 0.677 eV, confirming the semiconducting nature of the ground state. This quantitative difference reflects the distinct treatments of electron correlation. More importantly, regardless of the quantitative method‐dependence, the band structure of CrScCO 2 proves to be highly tunable by external fields. Both strain and a vertical electric field can effectively modulate and even close this gap, driving the system into half‐metallic and, crucially, spin‐gapless semiconductor (SGS) states. This demonstrates that although CrScCO 2 exhibits a moderate band gap at the hybrid functional level, its electronic structure is susceptible to external perturbations, enabling a transition into the SGS regime under appropriate modulation. This material demonstrates good thermal stability at room temperature, showing potential as a tunable functional material in low‐power spintronic devices.