Superconductivity in Ag_xTaS₂ single crystals with stage structure obtained via proton-driven ion introduction

Ag⁺ ions were intercalated into the transition-metal dichalcogenide TaS₂ using the recently developed method of proton-driven ion introduction. Single-crystalline Ag_0.58TaS₂ with a stage 1 structure and Ag_0.21TaS₂ with a stage 2 structure were prepared using this method. The stage 2 structure of Ag_0.21TaS₂ was formed by exploiting the differences in ion diffusion properties among the polytypes of TaS₂. Furthermore, our intercalation method can forcibly insert Ag⁺ ions into interlayers by applying a high voltage at low temperature (100°C), resulting in the formation of thermodynamically metastable phase. Such a synthesis approach offers a potential route for diversifying intercalation compounds with different stage structures. The first observations of superconductivity in Ag_xTaS₂ were demonstrated in this study. The onset of superconductivity of Ag_xTaS₂ was estimated to be 0.4 and 1.7 K in the samples with x = 0.58 and x = 0.21, respectively. Some anomalies, which were speculatively attributed to charge density wave order, were confirmed in the resistivity measurements of Ag_xTaS₂. The results suggested that the anomalies were closely correlated with the superconducting transition temperature.