S. Y. Zhou, H. Zhang, X. C. Hong, B. Y. Pan, X. Qiu, W. N. Dong, X. L. Li, S. Y. Li
We report thermal conductivity measurements down to 50 mK on
Ca$_3$Ir$_4$Sn$_{13}$ single crystals, in which superconductivity with $T_c
\approx 7$ K was claimed to coexist with ferromagnetic spin-fluctuations. In
zero magnetic field, no residual linear term $\kappa_0/T$ is found. In low
magnetic fields, $\kappa_0(H)/T$ shows a slow field dependence. These results
demonstrate that the superconducting gap of Ca$_3$Ir$_4$Sn$_{13}$ is nodeless,
thus rule out an exotic nodal gap caused by ferromagnetic spin-fluctuations.
The relatively fast increase of $\kappa_0(H)/T$ near the upper critical field
$H_{c2}$ may result from gap anisotropy, or multiple isotropic gaps with
different magnitudes.
View original:
http://arxiv.org/abs/1202.5164
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