Theoretical evidence of the spin-valley coupling and valley polarization in two-dimensional MoSi2X4 (X = N, P, and As)

Very recently, the centimeter-scale MoSi2N4 monolayer was synthesized experimentally and exhibited a semiconducting nature with high mobility (Hong et al., Science, 2020, 369, 670-674). Here, we show that MoSi2N4 and its analogues, MoSi2P4 and MoSi2As4, are potential two-dimensional (2D) materials for valleytronics based on first-principles calculations. We demonstrate that the intrinsic inversion symmetry breaking and strong spin-orbital coupling lead to the remarkable spin-valley coupling in the inequivalent valleys at K and K ' points, which result in not only the valley-contrasting transport properties, but also the spin and valley coupled optical selection rules. Moreover, the in-plane strain can tune the bandgaps and spin splitting or even induce an indirect-to-direct bandgap transition for promising application in the strain-tunable valleytronics. We find that the valley polarization can be generated by doping magnetic element. Our findings offer theoretical insight into the exotic physical properties of novel MoSi2N4-family materials beyond transition metal dichalcogenides.

Automated summary

The centimeter-scale MoSi2N4 monolayer has been successfully synthesized and shown to exhibit high mobility as a semiconductor. MoSi2N4 and its analogues, MoSi2P4 and MoSi2As4, are potential 2D materials for valleytronics with unique spin-valley coupling properties. Intrinsic inversion symmetry breaking and strong spin-orbital coupling in the inequivalent valleys contribute to valley-contrasting transport properties and optical selection rules, with potential applications in strain-tunable valleytronics.