  Opening a band gap and realizing static valley control have been long sought
after in graphenebased two-dimensional (2D) materials. Motivated by the recent
success in synthesizing 2D materials passivated by Si-N layers, here, we
propose two new graphene-based materials, 2D C2SiN and CSiN, via
first-principles calculations. Monolayer C2SiN is metallic and realizes
superconductivity at low temperatures. Monolayer CSiN enjoys excellent
stability and mechanical property. It is a semiconductor with a ternary valley
structure for electron carriers. Distinct from existing valleytronic platforms,
these valleys can be controlled by applied uniaxial strain. The valley
polarization of carriers further manifest as a pronounced change in the
anisotropic conductivity, which can be detected in simple electric measurement.
The strong interaction effects also lead to large exciton binding energy and
enhance the optical absorption in the ultraviolet range. Our work opens a new
route to achieve superconductivity, ternary valley structure, and semiconductor
with enhanced optical absorption in 2D materials.
