High-Tc AgxBC and CuxBC superconductors accessible via topochemical reactions

Abstract

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 the intrinsically hole-doped AgBC possesses a unique combination of electronic and vibrational features to exhibit two-gap superconductivity above 50 K.