Superconductivity in iron silicideLu2Fe3Si5probed by radiation-induced disordering

Abstract

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 ...

Electronic structure and Fermi surface of iron-based superconductors R2Fe3Si5 (R = Lu;Y;Sc) from first principles

“…Nevertheless, any unconventional (non-phononic) mechanism of their superconductivity may be similar to those already postulated for a majority of iron-based compounds. These conclusions are in accord with the findings of recent various experiments presented in [28][29][30][31][32]. …”

“…The anisotropy of their superconducting properties, anomalous upper critical fields (in Lu2Fe3Si5), and inter-band electron scattering in the case of two weak-coupled distinct gaps opened on the whole Fermi surface (FS) sheets, indicated that they are rather quasi-2D superconductors [26][27][28][29]. Furthermore, some recent works [30][31][32] focused on the effect of doping by non-magnetic impurities and atomic disorder induced by the neutron irradiation, both causing a fast suppression of TC in Lu2Fe3Si5, have questioned the conventional (phononic) mechanism of SC in the (Lu;Y;Sc)2Fe3Si5 family, revealing the significance of spin fluctuations in formation of the SC state [32]. The same effect was observed in the high-TC (oxy)pnictides after irradiation and, hence, it might be universal for all iron-based superconductors.…”

Prediction of inorganic superconductors with quasi-one-dimensional crystal structure

“…As a result, the stack of Fe1 4 and Lu 4 squares alternating along the axis с can be considered as a corrugated metal tube. Inside this tube, chains of So far, the role of Fe and Lu atoms in the emergence of superconductivity has remained partially unclear [50][51][52][53][54]. If just 3d-electrons of Fe are responsible for superconductivity, this superconducting fragment must be considered as a stack of metal clusters Fe1 4 with chains of Si3 atoms inside it and Lu, Si1, and Si2 atoms outside it.…”

The electronic structure of rare-earth iron silicide R2Fe3Si5 superconductors

“…The interband electron scattering between these two weak-coupled gaps opened on the whole Fermi surface (FS) is the reason for an observed anisotropy of superconducting properties in the 235-type iron silicides being rather quasi-2D superconductors [24,25,26,27,28,29]. Furthermore, the conventional (phononic) character of an SC mechanism in Lu 2 Fe 3 Si 5 has been questioned by a fast suppression of T c caused by non-magnetic impurities and atomic disorder induced by the neutron irradiation [30,31,32]. These effects might be explained by spin-fluctuation mediated scenario of SC, similarly to that postulated in iron (oxy)pnictides.…”