Specific heat has been investigated in a layered nitride superconductor, ${\mathrm{Li}}_{0.12}\mathrm{ZrNCl}$, with $T_c=12.7\mathrm{K}$. The obtained data have shown a marked dichotomy: The specific heat jump at $T_c$ ($\Delta C/{\gamma }_n{T}_c=1.8$) and the superconducting gap ratio ($2\Delta /k_B{T}_c=4.6–5.2$) have indicated an intermediate to a strong coupling of electrons, while the upper limit of the electron-phonon coupling constant $\lambda$ has directly been estimated to be 0.22, which belongs to a weak coupling regime. Furthermore, the rapid increase of $\gamma$ as a function of magnetic field suggests that the present material has an anisotropic $s$ wave gap.

• Received 26 January 2005

DOI:https://doi.org/10.1103/PhysRevLett.94.217002