Point Contact Spectroscopy in Doped Iron Pnictide Superconductors

We report results of ongoing experiments that probe the superconducting energy gap of iron-based superconducting pnictide single crystals that use silver paint for soft point contacts. These measurements use nanometer-size gold wires pressed against crystals and lead to transport mechanisms within the ballistic regime. Using this technique, we have previously reported evidence for multi-gap features in underdoped Ba (1-x) K x Fe 2 As 2 single crystals where we observed temperature-dependent gaps of Δ 1 = 2-4 meV and Δ 2 = 9-11 meV that correspond to directional tunneling through the ab – axes. In current measurements, we have used point contact spectroscopy to study P-doped and similar pnictide samples to look for similar features. These measurements were performed by undergraduates.