Designing Organic Spin-Gapless Semiconductors via Molecular Adsorption on C₄N₃ Monolayer

Spin-gapless semiconductor (SGS), a class of zero-gap materials with fully spin-polarized electrons and holes, offers significant potential for high-speed, low-energy consumption applications in spintronics, electronics, and optoelectronics. Our first-principles calculations revealed that the Pca21 C₄N₃ monolayer exhibits a ferromagnetic ground state. Its band structure displays SGS-like characteristics, with the energy gap between the valence and conduction bands near the Fermi level in the spin-down channel much smaller than the one in the other spin channel. To enhance its SGS properties, we introduced electrons into the Pca21 C₄N₃ monolayer by adsorbing the CO gas molecule on its surface. Stable gas adsorption (CO@C₄N₃) effectively narrowed the band gap in the spin-down channel without changing the band gap in the spin-up channel obviously. Moreover, injecting holes into the CO@C₄N₃ system could increase the net magnetic moments and induce an SGS-to-metallic phase transition, while injecting electrons into the CO@C₄N₃ system is able to lower the net magnetic moments and cause an SGS-to-half-metallic phase transition. Our findings not only underscore a new promising material for practical metal-free spintronics applications but also illustrate a viable pathway for designing SGSs.