Triggering superconductivity, semiconducting states, and ternary valley structure in graphene via functionalization with Si-N layers

Abstract

Opening a band gap and realizing static valley control have been long sought in graphene-based 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 ${\mathrm{C}}_{2}\mathrm{SiN}$ and CSiN, via first-principles calculations. Monolayer ${\mathrm{C}}_{2}\mathrm{SiN}$ is metallic and realizes superconductivity at low temperatures. Monolayer CSiN enjoys excellent stability and a 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 manifests 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 paper opens a new route to achieve superconductivity, ternary valley structure, and a semiconductor with enhanced optical absorption in 2D materials.