Superconductivity in a three-dimensional kagome-like boron allotrope

We design a three-dimensional kagome-like boron allotrope, referred to as 3D kagome boron, with boron tetrahedron as the building block. By means of density-functional first-principles calculations, we find that 3D kagome boron is dynamically stable and shows metallic behavior within a near-ambient pressure ranging from 7 to 13 GPa. The electronic structure of 3D kagome boron is insensitive to pressure, while acoustic phonons become stiffened with increasing pressure. Based on the Wannier interpolation technique, we investigate the electron-phonon coupling (EPC) superconductivity in 3D kagome boron. The EPC constant $\ensuremath{\lambda}$ is calculated to be 0.91 and 0.74 under 7 and 13 GPa, respectively. By solving anisotropic Eliashberg equations, the superconducting transition temperature (${T}_c$) is determined to be $\ensuremath{\sim}35\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ under 7 GPa. With increasing pressure, we find that the EPC matrix element weakens and acoustic phonons stiffen, which causes a lower superconducting ${T}_c\ensuremath{\sim}30\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ under 13 GPa. We also find that 3D kagome boron possesses a wide superconducting region ranging from 7 to 50 GPa, as well as showing a robust high ${T}_c$ which is higher than 15 K throughout. The 3D kagome boron predicted here exhibits a high superconducting ${T}_c\ensuremath{\sim}35\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ under 7 GPa, which is the elemental superconductor with the highest superconducting ${T}_c$ within a pressure of 20 GPa and almost comparable to the highest superconducting ${T}_c$ of 36 K of elemental Sc under 260 GPa.