Exploring quadratic nodal point and square nodal line in two dimensional binary C4X2 compounds (X = N, P, As)

Recently, the investigation of topological states in two dimensional materials has gained prominence, serving as a complementary area to studies of three dimensional systems. This research presents the exceptional topological properties of the monolayer binary compounds C₄X₂ (X = N, P, As) through theoretical calculations. These compounds are characterized by a simple electronic structure consisting of only two bands near the Fermi energy and their band crossing leads to noteworthy topological features, specifically a quadratic nodal point and a Weyl square nodal line. A comprehensive analysis of the mechanisms underlying band formation and dispersion conditions has been conducted. The edge states associated with these compounds emerge from the nodal point and extend towards the nodal line, exhibiting extensive spatial distribution. The lightweight constituent elements of these materials ensure that both the topological features and edge states maintain stability, even when accounting for spin-orbit coupling effects. To enhance practical applicability, this study has also assessed the strain-dependent behaviors of the topological states alongside the anisotropic mechanical properties of the materials. Collectively, the investigation of these ideal topological states, in conjunction with the stability of the material candidates, lays a robust foundation for future experimental research. This work has the potential to facilitate significant advancements in the rapidly evolving field of two-dimensional topological materials.