Enhanced superconductivity in bilayer kagome borophene by alkali and alkaline earth metal deposition

The successful synthesis of bilayer borophene has stimulated interest in further research on boron-based materials. Recently, Gao $et \mathit{al}$. predicted a new bilayer kagome borophene (BK-borophene) with multiple van Hove singularities [Adv. Sci. 11, 2305059 (2024)]. The peculiar influence of van Hove singularities on material properties arouse our curiosity for in-depth research on this material. Here, we regulate the properties of BK-borophene by depositing alkali and alkaline earth metal elements on one side of it and named them as $M$-BK-borophenes. Based on first-principles calculations, we analyze their dynamic and thermodynamic stability and find only two $M$-BK-borophenes ($M=\mathrm{Mg}$, Ca) to be stable at room temperature and ambient pressure. The electronic structures of Mg- and Ca-BK-borophene show that as an electron donor, Mg and Ca change the electron distribution and electron-phonon coupling of BK-borophene, enhancing their superconductivity with stronger EPC strengths of 0.97 and 0.59, as well as superconducting transition temperatures of 29.1 and 18.7 K, which is higher than the reported bilayer borophenes with an intact bilayer boron structure. Therefore, the predicted $M$-BK-borophenes ($M$ = Mg, Ca) provide platforms for the stability, electronic property regulation, and two-dimensional superconductivity realization in BK-borophene.