Nodeless superconductivity in Ca3Ir4Sn13: evidence from quasiparticle heat transport

TL;DR

This study investigates the superconducting gap structure of Ca3Ir4Sn13, providing evidence that it is nodeless through thermal conductivity measurements, challenging previous claims of coexistence with ferromagnetic spin-fluctuations.

Contribution

The paper presents thermal conductivity data indicating nodeless superconductivity in Ca3Ir4Sn13, clarifying the nature of its gap structure and its relation to magnetic fluctuations.

Findings

Residual linear term in thermal conductivity is negligible, indicating a nodeless gap.

Superconductivity shows a slow field dependence of thermal conductivity.

Resistivity behavior varies among crystals, with some showing Fermi-liquid behavior.

Abstract

We report resistivity $\rho$ and thermal conductivity $\kappa$ measurements 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. Among three crystals, only one crystal shows a small hump in resistivity near 20 K, which was previously attributed to the ferromagnetic spin-fluctuations. Other two crystals show the $\rho \sim T^2$ 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 Ca$_3$Ir$_4$Sn$_{13}$ is nodeless, thus rule out nodal gap caused by ferromagnetic spin-fluctuations.