We grew the single crystals of the SnAs-based van der Waals (vdW)-type superconductor NaSn2As2 and systematically measured its resistivity, specific heat, and ultralow-temperature thermal conductivity. The superconducting transition temperature Tc = 1.60 K of our single crystal is 0.3 K higher than that previously reported. A weak but intrinsic anomaly situated at 193 K is observed in both resistivity and specific heat, which likely arises from a charge-density-wave (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 κ0/T further suggests NaSn2As2 is an s-wave superconductor.
@article{arxiv.1806.01141,
title = {Nodeless superconductivity in the SnAs-based van der Waals type superconductor NaSn2As2},
author = {E. J. Cheng and J. M. Ni and F. Q. Meng and T. P. Ying and B. L. Pan and Y. Y. Huang and Darren Peets and Q. H. Zhang and S. Y. Li},
journal= {arXiv preprint arXiv:1806.01141},
year = {2018}
}