title: Two-gap superconductivity inR2Fe3Si5(R=Lu, Sc) and Sc5Ir4Si10.
abstract: R2Fe3Si5(R= Sc, Y, Lu) contains nonmagnetic iron and has a relatively high superconducting transition temperatureTcamong iron-containing superconductors. An anomalous temperature dependence of specific heatC(T) has been reported for polycrystalline samples down to 1 K. We have grownR2Fe3Si5single crystals, confirmed the anomalousC(T) dependence, and found a second drop in specific heat below 1 K. In Lu2Fe3Si5, we can reproduceC(T) belowTc, assuming two distinct energy gaps 2Δ1/kBTc= 4.4 and 2Δ2/kBTc= 1.1, with nearly equal weights, indicating that Lu2Fe3Si5is a two-gap superconductor similar to MgB2. Hall coefficient measurements and band structure calculation also support the multiband contributions to the normal-state properties. The specific heat in the Sc2Fe3Si5single crystals also shows the two-gap feature.R5Ir4Si10(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 Sc5Ir4Si10single crystals and found thatC(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.
authors.affiliation: Department of Applied Physics, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Tamegai
authors.affiliation: Department of Applied Physics, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Nakajima
authors.affiliation: Department of Applied Physics, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Nakagawa
authors.affiliation: Department of Applied Physics, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
authors.forename: Guoji
authors.initials: G
authors.lastname: Li
authors.affiliation: Department of Physics, Kobe University, Kobe 657-8501, Japan.
authors.forename: Hisatomo
authors.initials: H
authors.lastname: Harima
keywords: Lu2Fe3Si5; Sc2Fe3Si5; Sc5Ir4Si10; two-gap superconductivity