Superconductivity in two-dimensional boron allotropes

We use ab initio evolutionary algorithm and first-principles calculations to investigate structural, electronic, vibrational, and superconducting properties of two-dimensional (2D) boron allotropes. Remarkably, we show that conventional BCS superconductivity in the stable 2D boron structures is ubiquitous with the critical temperature Tc above the liquid hydrogen temperature for certain configurations. Due to the electronic states of the Fermi surface originating from both σ and π electrons, the superconductivity of the 2D structures arises from multiple phonon modes. Our results support that 2D boron structure may be a pure single-element material with the highest Tc on conditions without high pressure and external strain.