Electron-phonon interaction and superconductivity of potassium-intercalated hexagonal boron nitride

Potassium intercalated hexagonal boron nitride is known to be metallic and was recently synthesized using a straightforward molten-metal-assisted approach. First-principles calculations suggest that the resulting compound consists of one or two potassium layers between hBN layers. The potassium electron disperses in space, forming a nearly free 2D electron gas between hBN layers with a corresponding parabolic conduction band. At 0.7 eV above the Fermi level there is nearly flat boron π band, which is found to be critical for superconductivity. We study how the hBN interlayer distance and doping move this band closer to the Fermi level and show that it can result in T_c as high as several dozen Kelvins in an ideal scenario, using density functional perturbation theory and anisotropic Migdal-Eliashberg theory. We also show that boron and nitrogen vacancies can be beneficial for the higher electron phonon coupling and hence superconductivity.