Suppression of the critical temperature of superconducting Ba ( Fe 1 − x Co x ) 2 As 2 by point defects from proton irradiation

We report the effect of 3 MeV proton irradiation on the suppression of the critical temperature T-c in Ba(Fe1-xCox)(2)As-2 single crystals at underdoping, optimal-doping, and overdoping levels. We find that T-c decreases and residual resistivity increases monotonically with increasing dose. We also find no upturn in low-temperature resistivity in contrast with the alpha-particle- irradiated NdFeAs(O,F), which suggests that defects induced by the proton irradiation behave as nonmagnetic scattering centers. The critical scattering rate for all samples estimated by three different ways is much higher than that expected in s(+)-pairing scenario based on interband scattering due to antiferromagnetic spin fluctuation.