PACS: 74.70._b, 74.62.Dh, 72.15.Gd. Resistivity ρ(T), Hall coefficient R H (T), superconducting temperature T c , and the slope of the upper critical field −dH с2 /dT were studied in poly-and single-crystalline samples of the Fe-based superconductor Lu 2 Fe 3 Si 5 irradiated by fast neutrons. Atomic disordering induced by the neutron irradiation leads to a fast suppression of T c similarly to the case of doping of Lu 2 Fe 3 Si 5 with magnetic (Dy) and non-magnetic (Sc, Y) impurities. The same effect was observed in a novel FeAs-based superconductor La(O-F)FeAs after irradiation. Such behavior is accounted for by strong pair breaking that is traceable to scattering at non-magnetic impurities or radiation defects in unconventional superconductors. In such superconductors the sign of the order parameter changes between the different Fermi sheets (s ± model). Some relations that are specified for the properties of the normal and superconducting states in high-temperature superconductors are also observed in Lu 2 Fe 3 Si 5 . The first is the relationship −dH c2 /dT ~ T c , instead of the one expected for dirty superconductors −dH c2 /dT ~ ρ 0 . The second is a correlation between the low-temperature linear coefficient a in the resistivity ρ = ρ 0 + a 1 T, which appears presumably due to the scattering at magnetic fluctuations, and T c ; this correlation being an evidence of a tight relation between the superconductivity and magnetism. The data point to an unconventional (non-fononic) mechanism of superconductivity in Lu 2 Fe 3 Si 5 , and, probably, in some other Fe-based compounds, which can be fruitfully studied via the radiation-induced disordering.The discovery of high-temperature superconductivity in layered iron-based compounds [1] stimulated active experimental and theoretical studies of these systems in view of the possibility of the Cooper pairing of charge carriers by an anomalous type. Hence, a systematic study of the disordering effects in new superconductors is especially important [2]. According to the Anderson theorem [3], nonmagnetic impurities do not cause a suppression of the superconductivity in the case of a conventional s-type isotropic pairing. If the singlet pairing is traceable to the exchange of spin excitations, the requirement for this is the symmetry with a sign-changing order parameter [4]. Evidently, such requirement is fulfilled in high-T c cuprates, where pairing with d-wave symmetry is realized, while the pairing process proper is destroyed by an intraband scattering at nonmagnetic centers [4,5,6]. In the FeAs-based superconductors, the ordering parameter has the s-type symmetry, therefore a generally accepted is the s ± -model, which treats a superconducting state with the opposite signs of the ordering parameter for electrons and holes [7,4,8,9]. In this case nonmagnetic scatters must lead to the suppression of superconductivity due to the interband scattering between the electron-and hole-type Fermi surfaces [4,5,10]. Thus, the study of the atomic disordering in superconducting ...
