Tunneling spectroscopy of layered nitride superconductors MNCl0.7 (M = Hf and Zr)

Abstract

We have carried out tunneling measurements for MNCl0.7 (M=Hf and Zr) with Tc∼24K and ∼14K, respectively, using break-junction technique. Observed gap structures can be reproduced by the superconductor–insulator–superconductor (SIS) conductance with the BCS density of states. The estimated gap ratio 2Δ/kBTc⩾5 for both compounds is turned out to be larger than that of the conventional superconductors.