High-Temperature Phonon-Mediated Superconductivity with T_c above 100K in Monolayer Na(BC)₂ and K(BC)₂

Abstract Two-dimensional (2D) materials have demonstrated promising prospects owing to their distinctive electronic properties and exceptional mechanical properties. Among them, 2D superconductors with T_c above the boiling point of liquid nitrogen (77 K) will exhibit tremendous applicable value in the future. Here, we design two 2D superconductors Na(BC)₂ and K(BC)₂ with MgB₂-like structures, which are theoretically predicted to host T_c as high as 99 and 102 K, respectively. The origin of such high T_c is ascribed to the presence of both σ-bonding bands and van Hove singularity at the Fermi level. Furthermore, T_c of Na(BC)₂ is boosted up to 153 K with a biaxial strain of 5%, which sets a new record among 2D superconductors. The predictions of Na(BC)₂ and K(BC)₂ open the door to explore 2D high-temperature superconductors and provide a potential future for developing new applications in 2D materials.