Point Contact Spectroscopy of Iron Pnictides: Probing Superconductors to Observe the Gap Structures of Phosphorus Doped Iron Pnictides

We used a four-wire point contact spectroscopy system to obtain differential conductance (dI/dV) measurements in order to observe the energy gap structures of phosphorus doped iron-pnictides (x ~ 0.2 - 0.7) at 2K. We were motivated to study the phosphorus doped family of iron pnictides because our initial literature searches indicated that not many groups had taken differential conductance measurements of this family in order to identify gap structures, and also because the iron pnictides can exhibit multi-gap structures like those of magnesium di-boride. Our goal was to obtain the differential conductance measurements for varying x values of phosphorus, and observe the gap structures to further characterize and understand the superconducting transition of these iron pnictides. We observed both single and double gap structures for various x values, with delta 1 ~ 2-5 meV, and delta 2 ~ 7-10 meV. However, there were some interesting measurements in which we observed a possible delta 2 much further out than normal, at around 17-20 meV.