Unconventional superconductivity in electron-doped layered Li0.48(THF)yHfNCl

We report magnetic susceptibility measurements on a layered superconductor Li-0.48(THF)(0.3)HfNCl having T-c similar to 26 K. The present study revealed that (a) the Fermi level density of states is small, N*(E-F) - 0.25 states/(eV spin f.u.), (b) mass enhancement is negligible, <()over tilde> similar to 1, (c) electron-phonon coupling is weak, lambda (ep) much less than 1, (d) exchange enhancement is negligible, 1/(1 + F-0(a)) similar to 1, and (e) electronic density parameter is large, r(s)(2D) similar to 10.3 (i.e., low-carrier density). It is difficult to explain the origin of the high T-c in terms of the conventional phonon (BCS) mechanism of superconductivity.