Duality in an electron-doped ZrNCl superconductor as revealed by specific heat measurement

We have synthesized single phase samples of Li-doped ZrNCl and investigated the superconducting properties of them. Especially, we have measured the specific heat of Li0.12ZrNCl sample with Tc=12.7K. It has been revealed that this material has a small Sommerfeld constant γ=1.0±0.1mJ/molK2. In addition, the dual nature of coupling strength has also been unveiled.: While electron–phonon coupling constant λ is estimated to be less than 0.22, superconducting gap ratio and specific heat jump at Tc indicate intermediate to strong coupling of the present superconductor.