First-principles exploration of superconductivity in intercalated bilayer borophene phases

We explore the emergence of phonon-mediated superconductivity in bilayer borophenes by controlled intercalation with elements from the groups of alkali, alkaline-earth, and transition metals, using systematic first-principles and Eliashberg calculations. We show that the superconducting properties are primarily governed by the interplay between the out-of-plane (${p}_{z}$) boron states and the partially occupied in-plane ($s+{p}_{x,y}$) bonding states at the Fermi level. Our Eliashberg calculations indicate that intercalation with alkaline-earth-metal elements leads to the highest superconducting critical temperatures (${T}_{c}$). Specifically, Be in ${\ensuremath{\delta}}_{4}$, Mg in ${\ensuremath{\chi}}_{3}$, and Ca in the kagome bilayer borophene demonstrate superior performance with ${T}_{c}$ reaching up to 58 K. Our study therefore reveals that intercalated bilayer borophene phases are not only more resilient to chemical deterioration, but also harbor enhanced ${T}_{c}$ values compared to their monolayer counterparts, underscoring their substantial potential for the development of boron-based two-dimensional superconductors.