%0 Journal Article
%T Andreev Reflection Like Enhancement Above Bulk $T_c$ in Electron Underdoped Iron Arsenides
%A H. Z. Arham
%A C. R. Hunt
%A J. Gillett
%A S. D. Das
%A S. E. Sebastian
%A D. Y. Chung
%A M. G. Kanatzidis
%A L. H. Greene
%J Physics
%D 2013
%I arXiv
%X 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.
%U http://arxiv.org/abs/1307.1908v1