Nodeless superconducting gap in the caged-type superconductors Y₅Rh₆Sn₁₈ and Lu₅Rh₆Sn₁₈

Low-temperature thermal conductivity measurements were performed on the single crystal of caged-type superconductors Y₅Rh₆Sn₁₈ and Lu₅Rh₆Sn₁₈ down to 80 mK. In zero magnetic field, no residual linear term is found for either superconductor. At low field, the of these two superconductors shows weak field dependence. These results exclude the nodal superconducting gap in Y₅Rh₆Sn₁₈ as revealed by recent specific heat measurements, and suggest that the caged-type superconductors R₅Rh₆Sn₁₈ (R = Y and Lu) may have a common nodeless superconducting gap.