Non-perturbative Super-exchange Interaction for High Curie Temperature in Intrinsic Magnetic Semiconductor
Here a non-perturbative super-exchange interaction is unveiled in co-valency scheme which allows long-range ferromagnetic exchange interactions, thus naturally gives intrinsic room-temperature ferromagnetic semiconductors. To realize such a scheme in transition metal compounds, two comparable energy scales are indispensable: i) the electron-electron interactions are comparable to the onsite energy difference between ligand p and metal d orbitals and ii) the hopping strengths between p and d orbitals are comparable to their band widths. Guided by these principles, a paradigm based on first-principles calculation and Wannier downfolding is then built to search for realistic materials. Through thorough physical parameter mining on 36 FeSe-like trilayer structures, CrAs monolayer is mapped out to belong to co-valency scheme, which possesses a band gap $\sim$ 0.45 eV, ferromagnetic nearest-/next-nearest-neighbor exchange coupling strength $\sim$ 57/40 meV, and correspondingly a high Curie temperature about 1500 K.