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Low-temperature thermal conductivity measurements were performed on single crystals of TlNi2Se2, a nickel chalcogenide heavy-electron superconductor with Tc ≃ 3.7 K. In zero field, the residual electronic contribution at T → 0 K (k0/T ) was well separated from the total thermal conductivity, which is less than 0.45% of its normal-state value. Such a tiny residual k0/T is unlikely contributed by the nodal quasiparticles. The nodeless gap structure is supported by the very weak field dependence of k0(H)/T in low magnetic fields. In the whole field range, k0(H)/T exhibits an S-shaped curve, as in the case of nickel pnictides BaNi2As2 and SrNi2P2. This common feature of nickel-based superconductors can be explained by multiple nodeless superconducting gaps. [ABSTRACT FROM AUTHOR]

The thermal conductivity of iron-based superconductor CsFe2As2 single crystal (Tc=1.81 K) was measured down to 50 mK. A significant residual linear term κ0/T=1.27 mW K-2 cm-1 is observed in zero magnetic field, which is about 1/10 of the normal-state value in upper critical field Hc2. In low magnetic field, κ0/T increases rapidly with field. The normalized κ0/T(H) curve for our CsFe2As2 (with residual resistivity ρ0=1.80 μΩ cm) lies between the dirty KFe2As2 (with ρ0=3.32 μΩ cm) and the clean KFe2As2 (with ρ0=0.21 μΩ cm), which is consistent with its impurity level. These results strongly suggest a nodal superconducting gap in CsFe2As2, similar to its sister compound KFe2As2. [ABSTRACT FROM AUTHOR]

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]

We report low-temperature heat transport measurements on superconducting iron sulfide FeS with Tc∷5 K, which has the same crystal structure and similar electronic band structure to the superconducting iron selenide FeSe. In zero magnetic field, a significant residual linear term κ0/T is observed. At low field, κ0/T increases rapidly with increasing field. These results suggest a nodal superconducting gap in FeS. We compare it with the sister compound FeSe and other iron-based superconductors with nodal gaps. [ABSTRACT FROM AUTHOR]