Interlayer-spacing dependence of Tc in LixMyHfNCl (M: molecule) superconductors.

We have systematically investigated the global phase diagram for Li{x}M{y}HfNCl (M: molecule), demonstrating the independent controllability of carrier density x and interlayer spacing d. In LixHfNCl, the superconducting phase with almost constant T{c} of 20 K prevails for 0.15<or<or.50. Accompanied by an increase in d upon the cointercalation, an enhancement of T{c} up to 30% was observed with its x independence preserved. This result indicates that pairing interaction strongly depends on the Fermi surface warping along the k{z} direction, implying the relevance of charge and/or spin fluctuation.