Enhanced superconductivity by Na doping in SnAs-based layered compound Na$_{1+x}$Sn$_{2-x}$As$_2$

TL;DR

This study shows that Na doping in SnAs-based layered compounds enhances superconductivity, increasing Tc from around 1.2-1.6 K to 2.1 K, and provides insights into defect energetics that favor doping.

Contribution

It demonstrates that Na doping on the Sn site effectively enhances Tc in NaSn₂As₂, revealing a new pathway to improve layered tin pnictide superconductors.

Findings

Na doping increases Tc up to 2.1 K

NaSn₂As₂ superconductivity is sensitive to non-stoichiometry

First-principles calculations favor Na doping over vacancies

Abstract

Superconducting transition temperature (Tc) reported in SnAs-based layered compound NaSn$_2$As$_2$ varies from 1.2 to 1.6 K, implying that its superconductivity is critically sensitive to non-stoichiometry. Here, we demonstrate that Na-doping on the Sn site (Na$_{1+x}$Sn$_{2-x}$As$_2$) is effective in enhancing superconductivity, leading to Tc = 2.1 K for x = 0.4. First-principles calculation indicates that such a doping, or Na$_{\rm Sn}$ antisite defects, is energetically favored over other cation vacancies. Our results pave the way for increasing Tc of layered tin pnictide superconductors.