Nodeless superconductivity in the SnAs-based van der Waals-type superconductor NaSn_2As_2

摘要

We grew the single crystals of the SnAs-based van derWaals (vdW)-type superconductor NaSn_2As_2 and systematically measured its resistivity, specific heat, and ultralow-temperature thermal conductivity. The superconducting transition temperature T_c = 1.60K of our single crystal is 0.3K higher than that previously reported. A weak but intrinsic anomaly situated at 193K is observed in both resistivity and specific heat, which likely arises from a charge-densitywave (CDW) instability. Ultralow-temperature thermal conductivity measurements reveal a fully gapped superconducting state with a negligible residual linear term in zero magnetic field, and the field dependence of κ_0/T further suggests NaSn_2As_2 is an s-wave superconductor.