Superconductivity in alkaline earth metal and Yb intercalated group VI layered dichalcogenides

Abstract

Alkaline earth metals and Yb have been intercalated into Group VI layered dichalcogenides, e.g., MoS₂, etc., by the liquid ammonia method at low temperatures. Chemical analysis and X-ray data indicate that ammonia is also intercalated along with the metal and that the c axis increases by ~3 Å in all the intercalated materials. In most cases, these compounds are only partially intercalated in that some pure unintercalated phase is present. Superconductivity has been observed in these intercalated compounds with the highest value T_onset of 5.7°K for Ba_x(NH₃)_yMoS₂; the T_onset temperatures depend on the nature of the metal and the host dichalcogenides but not on the concentration of the intercalated metal ion. Fine-particle (1-10 μm size) materials which are fully intercalated do not exhibit the superconductivity behavior as measured by the ac susceptibility method. The results are discussed in terms of the current band models for the Group VI MCh₂ materials and compared with alkali metal intercalated MoS₂ as reported by Somoano et al. (4).