A novel two-dimensional MgB₆ crystal: Metal-layer stabilized boron kagome lattice

Based on first-principles calculations, we designed for the first time a boron-kagome-based two-dimensional MgB₆ crystal, in which two boron kagome layers sandwich a triangular magnesium layer. The two-dimensional lattice is metallic with several bands across the Fermi level, and among them a Dirac point appears at the K point of the first Brillouin zone. This metal-stabilized boron kagome system displays electron-phonon coupling, with a superconductivity critical transition temperature of 4.7 K, and thus it is another possible superconducting Mg-B compound besides MgB₂. Furthermore, the proposed 2D MgB₆ can also be used for hydrogen storage after decoration with Ca. Up to five H₂ molecules can be attracted by one Ca with an average binding energy of 0.225 eV. The unique properties of 2D MgB₆ will spur broad interest in nanoscience and technology.