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

Abstract

Electronic structures of three superconducting rare-earth iron silicides (Lu;Y;Sc)2Fe3Si5 and nonsuperconducting Lu2Ru3Si5, adopting a tetragonal crystal structure (P4/mnc), have been calculated employing the full-potential local-orbital method within the density functional theory. The investigations were focused particularly on the band structures and Fermi surfaces, existing in four bands and containing rather threedimensional electronlike and holelike sheets. They support an idea of unconventional multi-band superconductivity in these ternaries, proposed earlier by other authors for Lu2Fe3Si5, based on heat-capacity, resistivity, electromagnetic and muon spin rotation measurements. Finally, a discussion on differences in the electronic structures between the investigated here and other common families of iron-based superconductors is carried out.

The electronic structure of rare-earth iron silicide R2Fe3Si5 superconductors

“…It is seen in this figure that the metallic character of the 235-type compounds originates from the wide Fe 3d electron peak centred at about 1.5 eV below E F . The DOS at the Fermi level, N(E F ), appears to be completely dominated by this kind of electrons in the whole family of the 235-type systems, similarly to our former results for (Lu;Y;Sc) 2 Fe 3 Si 5 [33]. The Si 3p electron orbitals hybridise with the Fe 3d orbitals, predominantly in the energy range of 1-6 eV below E F .…”

“…Our previous results for isoelectronic (Lu;Y;Sc) 2 Fe 3 Si 5 showed nearly equal DOSs at E F as well [33]. Also the DOSs in a small energy region around E F , depicted in Fig.…”

“…Former theoretical studies predicted multiband FSs of the 235-type iron superconductors, containing both electronlike and holelike pieces of different dimensionality and orbital character [19,33], in analogy to the most intensively investigated two-gap superconductor MgB 2 [34]. The differences in dimensionality of two FS sheets of this compound appeared to be crucial for its twoband SC phenomenon.…”

“…A former study showed that the Fe 3d electrons in this superconductor should play an important role in its SC phenomenon [33]. However, the substitution of other lanthanide atoms for Lu atomic positions leads to various effects: Tm 2 Fe 3 Si 5 and Er 2 Fe 3 Si 5 also exhibit SC, while Tb 2 Fe 2 Si 5 and Yb 2 Fe 2 Si 5 are non-superconducting, and in addition the latter is a HF system.…”

“…In the (Lu;Y;Sc) 2 Fe 3 Si 5 family, the larger gap may be connected with quasione-dimensional (quasi-1D) parts of the holelike FS sheets, while the socalled passive band may contribute to the 3D electronlike FS sheet [29]. Furthermore, in these superconductors, the orbital-dependent contributions of the Fe 3d electrons to the FSs are partially separated from one another [33]. It enables the possibility of a similar SC mechanism to that in iron (oxy)pnictides [35], however, of a much weaker character.…”