Two-Dimensional Chiral Covalent Organic Frameworks with Significant Rashba-Dresselhaus Spin Splitting.

Two-dimensional (2D) nonmagnetic semiconductors with large Rashba-Dresselhaus (R-D) spin splitting hold promise for applications in electric-field-controlled spintronics. Current research primarily focuses on metal-based R-D materials. A natural question is whether significant R-D spin splitting can be realized in metal-free organic systems. In this work, through first-principles calculations, we demonstrate that 2D chiral covalent organic frameworks (CCOFs) can serve as a potential platform for designing R-D semiconductors. By constructing 2D CCOFs with benzene cores and iodine-based chiral linkers, significant spin splitting at the valence band is achieved. Particularly, with 2,2'-diiodobiphenyl linkers, the R-D energy of spin splitting is 12 meV, accompanied by a coupling constant (α) of 0.12 eVÅ. Meanwhile, the spin texture of the valence band is adjustable via tuning the chirality. Furthermore, through group substitutions, the R-D energy can be notably increased up to 32 meV and the coupling constant up to 0.4 eVÅ, comparable to metal-based R-D materials.