The First Observation of Metallic Behaviour in Nd3.5Sm0.5Ni3O8

Abstract

In Nd3.5Sm0.5Ni3O8 which has basically the same crystal structure and the similar electrical configuration (Ni+ 3d 9/Ni2+ 3d 8 mix valence state) with high- T c cuprate, it has been found that this material shows metallic behaviour down to about 20 K by intercalation and subsequent deintercalation with sulfur. This is the first observation of the metallic state in this system. It is unclear why sulfur-intercalation and deintercalation induce the metallic state. We speculate that sulfur works as an effective getter for removing the interstitial apical oxygen which impedes the metallic conduction. However, the weak localization of carriers in the NiO2 planes still remains below 20 K and the localization may be one of the obstacles to occurrence of possible superconductivity.