Measurement of a Sign-Changing Two-Gap Superconducting Phase in Electron-Doped Ba(Fe_{1-x}Co_x)_2As_2 Single Crystals using Scanning Tunneling Spectroscopy

TL;DR

This study uses scanning tunneling spectroscopy to investigate electron-doped Ba(Fe_{1-x}Co_x)_2As_2 single crystals, revealing two-gap superconductivity with sign-changing s-wave symmetry and impurity scattering effects.

Contribution

It provides direct spectroscopic evidence of two-gap, sign-changing s-wave superconductivity in electron-doped BaFe2As2, highlighting the effects of doping and impurities.

Findings

Two-gap superconductivity confirmed in Ba(Fe_{1-x}Co_x)_2As_2

Gaps decrease with temperature and vanish above T_c

Impurity scattering influences superconducting properties

Abstract

Scanning tunneling spectroscopic studies of $Ba(Fe_{1-x}Co_x)_2As_2$ (x = 0.06, 0.12) single crystals reveal direct evidence for predominantly two-gap superconductivity. These gaps decrease with increasing temperature and vanish above the superconducting transition $T_c$. The two-gap nature and the slightly doping- and energy-dependent quasiparticle scattering interferences near the wave-vectors $(\pm \pi, 0)$ and $(0, \pm \pi)$ are consistent with sign-changing $s$-wave superconductivity. The excess zero-bias conductance and the large gap-to-$T_c$ ratios suggest dominant unitary impurity scattering.