Investigation by Undergraduates of the Superconducting Energy Gap of Ph-Doped and Co-Doped Iron Pnictides at 2-24 Kelvin*

The discovery of iron-based superconductors, where multiple superconducting energy gaps have been observed, has led to research studies of multi-band superconductivity. In these novel superconductors, the observed energy gaps are anisotropic and largely depend on the way that the crystal has been grown and how contact is made to access tunneling directions. In this work, we report the results of tunneling spectroscopy experiments on iron-pnictide crystals that were contacted using silver paint. We report the results of four-wire differential conductance measurements using two lock-in amplifiers of the energy gap of phosphorus-doped BaFe₂(As_1-x P_x)₂ where x = 0.204, 0.304, 0.25, 0.39, 0.43 and 0.69 and x = 0.08 for the cobalt-doped Ba(Fe_1-x Co_x)₂As₂. The differential conductance dI/dV of these samples exhibit broad peaks and shoulders with Δ 1 = 2-5 meV, and Δ 2 = 7-10 meV. Some of these results were reproducible over similar samples, correspond well with existing data from literature while other features appear new. We report temperature-dependent features that we are in the process of anayzing. These measurements were performed fully by undergraduates.