Two-gap superconductivity inR₂Fe₃Si₅(R=Lu, Sc) and Sc₅Ir₄Si₁₀

Abstract

R 2 Fe 3 Si 5 (R = Sc, Y, Lu) contains nonmagnetic iron and has a relatively high superconducting transition temperature T c among iron-containing superconductors. An anomalous temperature dependence of specific heat C(T) has been reported for polycrystalline samples down to 1 K. We have grown R 2 Fe 3 Si 5 single crystals, confirmed the anomalous C(T) dependence, and found a second drop in specific heat below 1 K. In Lu 2 Fe 3 Si 5 , we can reproduce C(T) below T c , assuming two distinct energy gaps 2 1 /k B T c = 4.4 and 2 2 /k B T c = 1.1, with nearly equal weights, indicating that Lu 2 Fe 3 Si 5 is a two-gap superconductor similar to MgB 2 . Hall coefficient measurements and band structure calculation also support the multiband contributions to the normal-state properties. The specific heat in the Sc 2 Fe 3 Si 5 single crystals also shows the two-gap feature. R 5 Ir 4 Si 10 (R = Sc, rare earth) is also a superconductor where competition between superconductivity and the charge-density wave is known for rare earths but not for Sc. We have performed detailed specific heat measurements on Sc 5 Ir 4 Si 10 single crystals and found that C(T) deviates slightly from the behavior expected for weak-coupling superconductors. C(T) for these superconductors can also be reproduced well by assuming two superconducting gaps.

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

“…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].…”

Specific Heat and Upper Critical Field of Sc5Ir4Si10Superconductor

“…where ( The two-gap model, which has been proved correct for another intermetallic compound Lu 2 Fe 3 Si 5 9) and may be applicable also in Sc 5 Ir 4 Si 10 , 12) contains two distinct gaps, . For the anisotropic s-wave, the gap structure can be expressed by , corresponding to the gap anisotropy min max / Δ Δ of 0.53±0.04, is shown in Fig.…”

“…Unfortunately, as far as we know little effort has been done on this issue. Tamegai et al 12) suggested that Sc 5 Ir 4 Si 10 may be a two-gap superconductor or only with weak gap anisotropy, while the intrinsic pairing mechanism and gap structure are still unknown.…”

“…The value of γ is roughly 0.45, reflecting the weakly one-dimensional Fermi surface, which is in consistent with the chainlike structure along the c-axis and the quasi-one-dimensional electronic band structure. 11,12,33,34) Actually, if we assume the Fermi velocities parallel to c-axis and ab plane are similar, according to the Ginzburg-Landau (GL) theory, 35,36) γ at T c is determined by the gap anisotropy. Thus, the gap anisotropy can be estimated as 0.45, which is in consistent with the value of 0.53 obtained from the specific heat.…”

Superconducting properties of the ternary transition-metal silicide Zr2Ru3Si4

“…In this period, superconductors with various attractive features have been discovered, such as the first heavy fermion superconductor (CeCu 2 Si 2 [2]), multigap superconductors (Lu 2 Fe 3 Si 5 [3,4] and Sc 5 Ir 4 Si 10 [5,4]) and a noncentrosymmetric superconductor (LaPtSi [6,1,7,8]). Reflecting these successful results, the efforts for searching new superconductors in R x T y Si z still have been continued until now.…”