Stability, Electronic Disruption, and Anisotropic Superconductivity of Hydrogenated Trilayer Metal Tetraborides (MB 4 H; M = Be, Mg, Ca, Al)

ABSTRACT The discovery of superconductivity in MgB 2 Tc = 39 K established metal diborides (MB 2 ) as a promising class of superconductors. Recent fabrication techniques have enabled the synthesis of 2D MgB 2 with a Tc of about 31 K, renewing interest in layered metal borides. This progress has led to predictions of superconductivity in 2D metal borides, including MB 4 (M = Be, Mg, Ca, Al), with CaB 4 exhibiting the highest estimated Tc of 36.1 K. Here, we show that hydrogenation can significantly enhance the superconducting transition temperature. We systematically investigate 2D hydrogenated trilayer metal borides (MB 4 H; M = Be, Mg, Ca, Al). These materials remain metallic, with states near the Fermi level dominated by boron p‐orbitals, while hydrogenation strongly modifies the band dispersion and Fermi surface topology. Phonon calculations confirm their dynamical stability and reveal strong electron–phonon interactions, leading to multi‐gap superconductivity. MgB 4 H, AlB 4 H, and CaB 4 H exhibit possible two‐gap behavior. CaB 4 H shows the strongest electron–phonon coupling, resulting in an intrinsic Tc of 64 K, whereas AlB 4 H shows the weakest coupling with Tc = 22 K. The electron–phonon coupling constants range from 0.62 to 0.99, demonstrating tunable superconductivity via elemental substitution.