Electronic properties and quasiparticle model of monolayer MoSi2N4

In this paper, we theoretically investigated the electronic properties of monolayer $\mathrm{Mo}{\mathrm{Si}}_{2}{\mathrm{N}}_{4}$ by combining first-principles calculations and symmetry analyses. Spin-orbital coupling resulted in band splitting, whereas a horizontal mirror symmetry constrained the spin polarization to be along the $z$ direction. In addition, a three-band tight-binding model was constructed to describe the low-energy quasiparticle states of monolayer $\mathrm{Mo}{\mathrm{Si}}_{2}{\mathrm{N}}_{4}$, which can be generalized to strained $\mathrm{Mo}{\mathrm{Si}}_{2}{\mathrm{N}}_{4}$ and its derivatives. The calculations using the tight-binding model showed an undamped $\sqrt{q}$-dependent plasmon mode, consistent with the results of first-principles calculations. The developed model is suitable for future theoretical and numerical investigations of low-energy properties in $\mathrm{Mo}{\mathrm{Si}}_{2}{\mathrm{N}}_{4}$ family materials. Furthermore, the study of the electronic properties of monolayer $\mathrm{Mo}{\mathrm{Si}}_{2}{\mathrm{N}}_{4}$ paves a way for its applications in spintronics and plasmonics.