Evolution of the Infinite Layer Superconducting Phase from the Perovskite Phase

The recent experimental report of elusive superconductivity in the infinite-layer nickelates has renewed interest in the field of high-T_c superconductors. Using soft-chemistry topotactic reduction method on doped perovskite nickelate thin films (using CaH₂), apical oxygen was successfully removed, resulting in the infinite layer superconducting phase. This process has not been understood well, and has been the source of irreproducibility in the field. The reported reduction parameters are mostly an estimate. Also, very little is understood about the intermediate states during the reduction. We have used a specially designed set up to perform in situ electrical measurements on the sample whilst the reduction is happening. We have found that the perovskite phase gets reduced to the superconducting phase through a very stable insulating intermediate state. The evolution and characteristics of the infinite layer from the perovskite through the various intermediate phases will be presented.