Monolayer ${\mathrm{SnS}}_2$ has emerged as a promising visible-light photocatalyst for photoelectrochemical applications, owing to its strong optical absorption in the visible range and excellent chemical stability. Despite its reduced dimensionality—where excitonic effects are expected to be pronounced—comprehensive theoretical investigations of bound excitons in this material remain scarce. Notably, unlike most two-dimensional hexagonal crystals, monolayer ${\mathrm{SnS}}_2$ exhibits its lowest single-particle transition at the $M$ point of the Brillouin zone (BZ). Here, the electronic valence bands form a saddle point while conduction states display a minimum with pronounced anisotropy, creating a distinctive band topology whose impact on optical excitations we systematically explore. In this work, we present a first-principles study of bound excitons in monolayer ${\mathrm{SnS}}_2$ based on state-of-the-art many-body perturbation theory, employing the $\mathit{GW}$ approximation and the Bethe–Salpeter equation. We analyze how band symmetry and anisotropy shape the excitonic wave functions and transition dipole moments. By resolving the exciton dipoles in momentum space for different linear light polarizations, we demonstrate that linearly polarized light lifts the $C_3$ rotational symmetry relating the three inequivalent $M$ points, giving rise to three linearly independent excitonic states. This polarization-selective coupling, previously identified for saddle points in graphene, is achieved in ${\mathrm{SnS}}_2$ for bound excitons and provides a potential route toward state encoding schemes in valleytronics applications.

Close

PrevNext

View figure in article

• Dielectric properties
• Electronic structure
• Excitons
• Monolayer films
• Density functional calculations
• GW method
• Many-body techniques