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arXiv · 1307.1908

Andreev Reflection Like Enhancement Above Bulk $T_c$ in Electron Underdoped Iron Arsenides

H. Z. Arham·C. R. Hunt·J. Gillett·S. D. Das·S. E. Sebastian·D. Y. Chung·M. G. Kanatzidis·L. H. Greene
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Abstract

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.

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H. Z. Arham, C. R. Hunt, J. Gillett, S. D. Das, S. E. Sebastian, D. Y. Chung, M. G. Kanatzidis, L. H. Greene. 2013-07-07. Andreev Reflection Like Enhancement Above Bulk $T_c$ in Electron Underdoped Iron Arsenides. https://arxiv.org/abs/1307.1908

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