Two-gap superconductivity in R 2 Fe 3 Si 5 ( R =Lu, Sc) and Sc 5 Ir 4 Si 10

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 Delta(1)/k(B)T(c) = 4.4 and 2 Delta(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.