Comparison study of superconductivity in zirconium and hafnium based electron-doped layered chloronitrides

The transition-metal chloronitrides form a fairly large family of superconductors. Motivated by the potential high-temperature superconductivity in electron-doped layered systems we investigated the thermodynamic properties of β-Li_0.5HfNCl and β-Li_0.5ZrNCl compounds. A systematic comparative study was carried out using the strong-coupling Eliashberg theory. In dependence on the chemical composition (Zr- or Hf-based system), a marked change in parameters of the superconducting state was observed. Moreover, the obtained results indicate that due to the existence of the strong-coupling and retardation effects the studied systems cannot be quantitatively described within the framework of classical Bardeen–Cooper–Schrieffer (BCS) theory