Nodeless superconductivity in Ca³lr4Sn13: Evidence from quasiparticle heat transport.

We report resistivity ρ and thermal conductivity K measurements on Ca³Ir4Sn13 single crystals, in which superconductivity with Tc ≈ 7 K was claimed to coexist with ferromagnetic spin fluctuations. Among three crystals, only one crystal shows a small hump in resistivity near 20 K, which was previously attributed to the ferromagnetic spin fluctuations. The other two crystals show the ρ ~ T² Fermi-liquid behavior at low temperature. For both single crystals with and without the resistivity anomaly, the residual linear term K0/ T is negligible in zero magnetic field. In low fields, K0(H)/T shows a slow field dependence. These results demonstrate that the superconducting gap of Ca3lr4Sn13 is nodeless and thus rule out a nodal gap caused by ferromagnetic spin fluctuations. [ABSTRACT FROM AUTHOR]