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

TL;DR

This study reports on the growth and comprehensive characterization of NaSn₂As₂, revealing nodeless s-wave superconductivity with a transition temperature of 1.60 K and evidence of a charge-density-wave instability.

Contribution

It provides the first detailed thermodynamic and transport measurements confirming nodeless superconductivity in NaSn₂As₂ and identifies a possible charge-density-wave phase.

Findings

Superconducting transition temperature T_c = 1.60 K.

Evidence of a charge-density-wave anomaly at 193 K.

NaSn₂As₂ exhibits fully-gapped s-wave superconductivity.

Abstract

We grew the single crystals of the SnAs-based van der Waals (vdW)-type superconductor NaSn$_2$As$_2$ and systematically measured its resistivity, specific heat, and ultralow-temperature thermal conductivity. The superconducting transition temperature $T_c$ = 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 $\kappa_0 / T$ further suggests NaSn$_2$As$_2$ is an $s$-wave superconductor.