Unconventional superconductivity in Li-intercalated layered nitride LixZrNCl

It is inferred from the temperature and magnetic field dependence of superfluid density that the gap parameter (2 Delta/k(B)T(c)) in LixZrNCl exhibits decrease with increasing x, suggesting development of anisotropic order parameter that leads to the reduction of Delta as a mean value. This observation is quantitatively in line with the d + id pairing predicted by recent theory based on the Hubbard model considering disconnected Fermi surfaces on a honeycomb lattice. (C) 2009 Elsevier B.V. All rights reserved.