Investigation of LiFeAs by means of "Break-junction" Technique

In our tunneling investigation using Andreev superconductor – normal metal – superconductor contacts on LiFeAs single crystals we observed two reproducible independent subharmonic gap structures at dynamic conductance characteristics. From these results, we can derive the energy of the large superconducting gap $\Delta_{\rm L}=(2.5{-}3.4)$ meV and the small gap $\Delta_{\rm L}=(0.9{-}1)$ meV at $T = 4.2$ K for the $T_{\rm C}^{\rm local} \approx (10.5{-}14)$ K (the contact area critical temperature which deviation causes the variation of $\Delta_{\rm L}$). The BCS-ratio is found to be $2\Delta_{\rm L}/k_{\rm B}T_{\rm C}=4.6{-}5.6$, whereas $2\Delta_{\rm S}/k_{\rm B}T_{\rm C}\ll3.52$ results from induced superconductivity in the bands with the small gap.