Quasiparticle scattering in 3 MeV proton irradiated BaFe2(As0.67P0.33) 2

Effects of 3 MeV H⁺ (proton) irradiation on superconductivity in BaFe₂(As_0.67P0.33)2 was investigated through in situ resistivity measurements and magnetotransport measurements. The suppression of T_c by H⁺ irradiation is more moderate in comparison with electron irradiation, yet more effective than that of irradiation of heavier He⁺ ions. Surprisingly, the B -linear magnetoresistance (MR) in the pristine crystal crosses over to an anomalous negative MR after the irradiation. We discuss that the negative MR is most likely to emanate from sparse magnetic impurities. The appearance of a paramagnetic signal in magnetization measurements supports the existence of magnetic impurities in the sample. Although the estimated concentration of local magnetic moments suggests that the concentration of magnetic impurities is dilute, thereby signifying that irradiation-induced defects are dominantly nonmagnetic, the role of magnetic scattering cannot be completely neglected. Hence, H⁺ irradiation in this system contains magnetic-scattering centers, which are pair breakers for both the s₊₊- and the s_±-gap structures, indicating that the suppression of T_c is a consequence of both magnetic and nonmagnetic scatterings. This result opens up the possibility for the scenario of the slow but steady suppression of T_c emanating from the s₊₊-gap symmetry with pair breaking due to dilute magnetic scatterers.