Optoelectrically controlled transistors in graphene-based valley-gapless, indirect-gap, and spin-valley-gapless semiconductors.

Generating and modulating fully spin-, valley-, and spin-valley-polarized currents are key to spintronics, valleytronics, and spin-valleytronics, respectively. Here, we propose optically controlled graphene-based multi-gapless semiconductors (SCs) for electrical modulation of such currents. The results reveal that antiferromagnetic exchange fields and a modified Haldane model induce valley-gapless SCs, which transition into four distinct spin-valley-gapless SCs under off-resonant circularly polarized light. Moreover, these gapless SCs, with the spin and valley degrees of freedom tunable via a gate voltage, are switched to indirect-gap SCs as the optical intensity increases. Consequently, under a gate voltage, optically modulated valley-gapless SCs, spin-valley-gapless SCs, and indirect-gap SCs, respectively give rise to fully spin-polarized currents, spin-valley-polarized currents, and an "off" state, thus enabling the realization of optoelectrically controlled transistors. Additionally, electrostatic potentials on leads further regulate current magnitude. Our work highlights the importance of these gapless SCs for optoelectrically controlled valleytronic and spin-valleytronic devices.