First-principles study on the superconductivity of doped zirconium diborides

Abstract

Recent experiments [Barbero et al. Phys. Rev. B 95, 094505 (2017)] have established that bulk superconductivity (Tc∼8.3–8.7K) can be induced in AlB2− type ZrB2 and HfB 2, highly covalent refractory ceramics, by vanadium (V) doping. These AlB2−structured phases provide an alternative to earlier diamondlike or diamond-based superconducting and superhard materials. However, the underlying mechanism for doping-induced superconductivity in these materials is yet to be addressed. In this paper, we have used first-principles calculations to probe electronic structure, lattice dynamics, and electron-phonon coupling (EPC) in V-doped ZrB2 and consequently examine the origin of the superconductivity. We find that, while doping-induced stress weakens the EPC, the concurrently induced charges strengthen it. The calculated critical transition temperature (Tc) in electron (and V)-doped ZrB2 is at least one order of magnitude lower than experiments, despite considering the weakest possible Coulomb repulsion between electrons in the Cooper pair, hinting a complex origin of superconductivity in it.