Abstract
We report the tunneling spectroscopy of non-oxide perovskite superconductor MgCNi3 polycrystals using a low-temperature scanning tunneling microscope. The obtained tunneling spectra clearly show a superconducting energy gap structure, which can be well fitted by the BCS function with smearing parameter [Gamma];. The value of the superconducting gap [Delta] is estimated to be 1.10-1.15 meV at 3 K, resulting in a ratio of 2[Delta]/kBTc=3.3-3.4 for Tc of 7.8 K. This result suggests that MgCNi3 is a conventional BCS s-wave superconductor in the weak-coupling regime.