High-Tc AgxBC and CuxBC superconductors accessible via topochemical reactions†

Hole-doping of covalent materials has long served as a blueprint for designing conventional high-T_c superconductors, but thermodynamic constraints severely limit the space of realizable compounds. Our ab initio results indicate that metastable Ag_xBC and Cu_xBC phases can be accessed via standard topochemical ion exchange reactions starting from Li_xBC precursors. Unlike all known stoichiometric layered metal borocarbides, the predicted AgBC and CuBC derivatives, comprising honeycomb layers bridged by dumbbells, are metallic rather than semiconducting. Anisotropic Migdal–Eliashberg analysis reveals that intrinsically hole-doped AgBC exhibits a unique combination of electronic and vibrational features to exhibit two-gap superconductivity above 50 K.