Superconductivity in AgxTaS2 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 Ag0.58TaS2 with a stage 1 structure and Ag0.21TaS2 with a stage 2 structure were prepared using this method. The stage 2 structure of Ag0.21TaS2 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 AgxTaS2 were demonstrated in this study. The onset of superconductivity of AgxTaS2 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 AgxTaS2. The results suggested that the anomalies were closely correlated with the superconducting transition temperature.