Tunneling Spectroscopy of Slightly Overdoped Pnictides BaFe\({}_{\mathbf{1.88}}\)Ni\({}_{\mathbf{0.12}}\)As\({}_{\mathbf{2}}\) in the Superconducting and Normal State

Abstract

The current study presents the results of tunneling spectroscopy measurements of current-voltage characteristics (CVC) and dynamic conductance spectra \(dI(V)/dV\) of SnS tunneling contacts in single crystals of slightly overdoped superconducting ferro-pnictide of nominal composition BaFe\({}_{1.88}\)Ni\({}_{0.12}\)As\({}_{2}\) with bulk critical temperature \(T_{c}=18\) K. Besides the Andreev structure, a strong nonlinearity is observed in the obtained curves both in the superconducting and normal state. The positions and temperature dependences of the observed \(dI(V)/dV\)-features unrelated to the superconducting state are determined for the temperature range \(4.3{-}26.4\) K. The paper analyzes possible reasons for the emergence of the observed features.