Superconductivity in R$_{3}$T$_{4}$Ge$_{13}$ (R $=$ Y, Lu and T $=$ Rh, Co, Os) single crystals

Single crystals of R$_{3}$T$_{4}$Ge$_{13}$ (R $=$ Y, Lu and T $=$ Rh, Co, Os) have been grown by flux methods and have been found to adopt the Pr$_{3}$Rh$_{4}$Sn$_{13}$ structure type. Magnetization and specific heat measurements confirm that all four compounds are bulk superconductors. Reduced superconducting gaps observed in the specific heat suggest that these may be multi-band superconductors. We observe an unusual increase of the electrical resistivity and a decrease of the charge carrier density on cooling in the normal state in all four reported compounds. However, band structure calculations reveal a metallic ground state in all four compounds, consistent with the emergence of superconductivity at low temperatures. We empirically show that large atomic displacement parameter ratios in R$_{3}$T$_{4}$Ge$_{13}$ compounds are correlated with the semiconduc tor-like behavior, resolving the contradiction between the experiment and the calculations.