Tunneling spectroscopy of the electron-doped layered superconductor Li0.48(THF)0.3HfNCl

Tunneling measurements on the electron-doped layered superconductor Li-0.48(THF)(0.3)HfNCl(THF;C4H8O) with T-c = 25.5 K have been carried out. Since the surface of this compound is very reactive, we have employed in situ break junction to obtain unaffected interface. The result shows the gap value of 2Delta = 9-12 meV, which leads to the strong-coupling gap ratio 2Delta/k(B)T(c) similar or equal to 5. This is the largest value among non-cuprate superconductors. (C) 2003 Elsevier Science B.V. All rights reserved.