Tunneling spectroscopy of slightly overdoped pnictides BaFe1.88Ni0.12As2 in the superconducting and normal state

Abstract

Using tunneling spectroscopy, we measured current-voltage characteristics (CVC) and dynamic conductance spectra 𝑑𝐼(𝑉 )/𝑑𝑉 of tunneling contacts in single crystals of slightly overdoped superconducting ferro-pnictide of nominal composition BaFe1.88Ni0.12As2 with bulk critical temperature 𝑇𝑐 = 16−18 K. Besides the Andreev structure, a strong nonlinearity is observed in the obtained curves both in the superconducting and normal state. For the temperature range 4.3 − 26.4 K we determined the positions and temperature dependences of the observed features irrelated to the superconducting state. Additionally, we discuss the possible origins for the appearance of the observed features.