Anisotropic superconducting order parameter in Li-intercalated layered superconductor LixZrNCl

In this study, it is shown that in a layered nitride superconductor, i.e., LixZrNCl(0.07 <= x <= 0.21), the superconducting order parameter is highly anisotropic in a sample with x=0.12, as inferred from both the temperature and the magnetic field dependences of the muon depolarization rate (sigma(s), proportional to the superfluid density). Moreover, the tendency of strong anisotropy with an increase in x is indicated by the T dependence of sigma(s). These observations are in good agreement with the recent theory that predicts the development of anisotropy in a d+id' gap upon carrier filling to the bands with disconnected Fermi surfaces on a honeycomb lattice.