Nodeless superconductivity in Ca3Ir4Sn13: Evidence from quasiparticle heat transport

We report resistivity rho and thermal conductivity. measurements on Ca3Ir4Sn13 single crystals, in which superconductivity with T-c approximate to 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 showthe rho similar to T-2 Fermi-liquid behavior at low temperature. For both single crystals with and without the resistivity anomaly, the residual linear term kappa(0)/T is negligible in zero magnetic field. In low fields, kappa(0)(H)/T shows a slow field dependence. These results demonstrate that the superconducting gap of Ca3Ir4Sn13 is nodeless and thus rule out a nodal gap caused by ferromagnetic spin fluctuations.