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.