The semihydrogenated bilayer graphene (${\mathrm{C}}_2{\mathrm{C}}_2\mathrm{H}$), which is a bilayer graphene semihydrogenated on one graphene layer, can be considered as the merging of a monolayer graphene and a semihydrogenated graphene (${\mathrm{C}}_2\mathrm{H}$) through the interlayer bonds. Based on this picture, and an approximation to the low-energy band of ${\mathrm{C}}_2\mathrm{H}$, we construct the low-energy effective model of ${\mathrm{C}}_2{\mathrm{C}}_2\mathrm{H}$. In both the nonmagnetic state and the magnetic ordered state, the low-energy effective model of ${\mathrm{C}}_2{\mathrm{C}}_2\mathrm{H}$ is equivalent to the model of ${\mathrm{C}}_2\mathrm{H}$. Similar to ${\mathrm{C}}_2\mathrm{H}$, the Berry curvature distributions in the low-energy bands of ${\mathrm{C}}_2{\mathrm{C}}_2\mathrm{H}$ concentrate close to the two valleys of the hexagonal Brillouin zone and have opposite signs at the two valleys. Because of the close connection between the Berry curvature distribution and the optical selection rule, the optical excitations under circularly polarized light are valley polarized in both the nonmagnetic state and the magnetic state. In the magnetic ordered state, the optical excitations are also spin resolved, and are therefore spin and valley coupled. By tuning the resonant energies of the two spin channels via a vertical electric field, the low-energy optical excitations under circularly polarized light can be switched to any one of the four spin-valley polarization channels, indicating that ${\mathrm{C}}_2{\mathrm{C}}_2\mathrm{H}$ is a two-dimensional magnetic material with promising spin- and valley-resolved optoelectronic applications.

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• Electronic structure
• Magnetic order
• Optoelectronics
• Valley degrees of freedom
• Bilayer graphene
• Hubbard model
• Mean field theory
• Tight-binding model