We use point contact spectroscopy (PCS) to probe the superconducting properties of electron doped $\rm{ Ba(Fe_{ 1-x}Co_x)_2As_2}$ ($\rm{ x = 0.05, 0.055, 0.07, 0.08}$) and hole doped $\rm{ Ba_{ 0.8}K_{ 0.2}Fe_2As_2}$. PCS directly probes the low energy density of states via Andreev reflection, revealing two distinct superconducting gaps in both compound families. Apart from the electron underdoped $\rm{ Ba(Fe_{ 1-x}Co_{ x})_2As_2}$, the excess current due to Andreev reflection for the compounds follows the typical BCS temperature dependence. For underdoped $\rm{ Ba(Fe_{ 1-x}Co_{ x})_2As_2}$, the temperature dependence of the excess current deviates from that of BCS, developing a tail at higher temperatures and surviving above bulk $T_c$. Possible explanations for this anomalous behavior are explored.
Categories: cond-mat.supr-con