First-Principles Investigation of a Two-Dimensional Magnesium Carbide Monolayer: Tunable Bandgap, Light Carriers, and Strain-Induced Topological and Semiconductor-to-Metal Transitions

In this study, we present a comprehensive theoretical investigation of the strain-dependent elastic, electronic, and optical properties of a novel two-dimensional (2D) magnesium carbide (Mg2C) monolayer using density functional theory. Our calculations confirm the high energetic, dynamic, and mechanical stability of the monolayer, highlighting its robustness and suitability for flexible electronic and nanomechanical applications. The electronic band structure analysis demonstrates that strain engineering significantly modulates the bandgap, with compressive strain reducing it and tensile strain increasing it, making the material highly adaptable for strain-controlled semiconductor devices, photodetectors, and nano-electronic applications. Furthermore, we find that compressive strain induces a topological phase transition, transforming the Mg2C monolayer from a normal insulator to a topological insulator, as evidenced by the band inversion and the emergence of a non-zero ℤ2 invariant. This opens up possibilities for utilizing this material in quantum spintronics and dissipationless electronic devices. The optical properties exhibit substantial strain-induced shifts, with variations in the dielectric function, absorption coefficient, and optical conductivity. Enhanced absorption in the visible to ultraviolet range and tunable optical conductivity suggest potential applications in optoelectronic devices, including photovoltaics, optical modulators, and sensors. The ability to fine-tune the electronic and optical properties through external strain makes this material highly promising for next-generation flexible and tunable optoelectronic technologies. Future experimental studies are encouraged to validate these theoretical predictions and explore real-time mechanical deformation effects, further expanding the potential applications of this intriguing 2D Mg2C monolayer.