Nodeless superconductivity in the SnAs-based van der Waals-type superconductor NaSn₂As₂

¹ State Key Laboratory of Surface Physics, Department of Physics, and Laboratory of Advanced Materials, Fudan University - Shanghai 200433, China
² Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, School of Physical Sciences, University of Chinese Academy of Sciences - Beijing 100190, China
³ Collaborative Innovation Center of Advanced Microstructures - Nanjing 210093, China

^(a) shiyan_li@fudan.edu.cn

Received: 25 May 2018
Accepted: 26 August 2018

Abstract

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 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 further suggests NaSn₂As₂ is an s-wave superconductor.