Effect of organic-molecule co-intercalation on T_c in Li_xHfNCl superconductor

The effect of dimethylformamide (DMF) co-intercalation on the T_c was investigated for Li_xHfNCl superconductors, in which carrier density x and interlayer distance d were controlled by changing the Li content and the size of the co-intercalated molecule, respectively. Upon the DMF co-intercalation, an enhancement of T_c was observed similarly to the previous results of other several organic molecules, showing a reasonable correlation between T_c and interlayer distance. This result is further evidence that pairing interaction among electrons sensitively, but systematically, depends on the Fermi surface warping along k_z direction, implying the relevance of charge- and/or spin-fluctuation.