Comparative Studies of Quasi-One-Dimensional Superconductivity in Sc$_{5}$Ir$_{4}$Si$_{10}$ and Lu$_{5}$Ir$_{4}$Si$_{10}$

Compounds with a formula $R_{5}T_{4}X_{10}$ ($R$=Sc, Y, rare earth elements, $T$=Co, Ir, Rh, Os, $X$=Si, Ge) crystallize in Sc$_{5}$Co$_{4}$Si$_{10}$--type structure with Sc-Si chains running along the $c$-axis. Some of them show superconductivity with relatively high transition temperatures and coexistence of superconductivity and charge-density wave. We have grown high quality single crystals of Sc$_{5}$Ir$_{4}$Si$_{10 }$and Lu$_{5}$Ir$_{4}$Si$_{10}$ using the floating-zone method. Thus obtained crystals show superior properties compared with polycrystalline materials, such as higher $T_{c}$ and $H_{c2}$. Anisotropic superconducting properties in these crystals are studied in detail. The upper critical field shows clear anisotropy, with $H_{c2}^{c }>H_{c2}^{ab}$, consistent with the quasi-one-dimensional crystal structure. Both compounds have modest anisotropies with $\gamma (=H_{c2}^{c }$/$H_{c2}^{ab}$ )=2.3 for Sc$_{5}$Ir$_{4}$Si$_{10}$ and $\gamma $=1.6 for Lu$_{5}$Ir$_{4}$Si$_{10}$. Magnetic penetration depths in Sc$_{5}$Ir$_{4}$Si$_{10}$ ($\lambda _{c}$= 900 A and $\lambda _{ab}$ =2100 A) estimated from the magnetic field dependence of the equilibrium magnetization confirm quasi-one-dimensional nature of the superconducting state.