Two-gap superconductivity in R2Fe3Si5 (R = Lu and Sc)

High-quality single crystals of Lu2Fe3Si5 and Sc2Fe3Si5 are grown by the floating-zone method, and their temperature dependences of specific heat are measured down to 0.35 K. Both compounds show anomalously small jump in specific heat at the superconducting transition temperature, Tc, and large residual specific heat coefficient even at 0.2 Tc, where BCS superconductor shows negligible electronic contribution. We also find drop in the specific heat coefficient below 0.2 Tc. These characteristics are very similar to MgB2, and temperature dependences of specific heat in both compounds are well reproduced by assuming two superconducting gaps. Upper critical field measurements confirm that both Lu2Fe3Si5 and Sc2Fe3Si5 are weakly one-dimensional superconductors.