  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.
