Floquet-engineered half-valley-metal state in two-dimensional gapped Dirac materials

The half-valley-metal (HVM) states where the gap of one valley is closed while the other valley remains semiconducting are quite crucial for achieving 100% valley polarization and valley-Hall-effect. However, the symmetry of materials makes the HVM states scarce. In this work, using Floquet theory, we demonstrate the laser-dressed HVM states in two-dimensional (2D) gapped-Dirac materials. We show that as a circularly polarized laser is applied to a 2D gapped-Dirac material, the gaps of the two valleys (K and K') can be regulated by varying the photon energy, amplitude and chirality of the laser. At specific photon energies and laser amplitudes, the linear energy-momentum dispersion of Dirac materials is restituted in one valley while the gap in the other valley is preserved. On the basis of first-principles calculations, we also propose a promising candidate material, boron antimonide (BSb) monolayer to achieve the laser-dressed HVM states. More interestingly, the Berry curvature in the two valleys can be tuned by changing the laser parameters.