Unexpected halogen-induced electron–phonon superconductivity in two-dimensional materials

Abstract

The VIIA halogen elements, with the greatest electronegativity, are generally repelled to emerge in conventional phonon-mediated superconductors governed by the electron–phonon coupling mechanism. Here we show by first-principles calculations the possibility of unusual halogen-induced high electron–phonon superconductivity exploiting a two-dimensional confinement system. We demonstrate that, in two unique models of fluorinated or chlorinated monolayers of MgB₂ and TiB₂, the F/Cl halogen adatoms, via realigning relevant surface electronic and low-frequency vibrational hybridizations, can strongly intensify the electronic density of states at the Fermi energy level and the electron–phonon coupling, and consequently boost transition temperatures of the intrinsically semi-metallic TiB₂ up to 20 K and of the superconducting MgB₂ from the primary 20 K to over 46 K. Our current results highlight a new way for designing high-T_c superconductors in a variety of versatile 2D nanomaterials.