Millimeter-scale Freestanding Superconducting Infinite-Layer Nickelate Membranes

Progress in the study of infinite-layer nickelates has always been highlylinked to materials advances. In particular, the recent development ofsuperconductivity via hole-doping was predicated on the controlled synthesis ofNi in a very high oxidation state, and subsequent topotactic reduction to avery low oxidation state, currently limited to epitaxial thin films. Here wedemonstrate a process to combine these steps with a heterostructure whichincludes an epitaxial soluble buffer layer, enabling the release offreestanding membranes of (Nd,Sr)NiO2 encapsulated in SrTiO3, which serves as aprotective layer. The membranes have comparable structural and electronicproperties to that of optimized thin films, and range in lateral dimensionsfrom millimeters to  100 micron fragments, depending on the degree of strainreleased with respect to the initial substrate. The changes in thesuperconducting transition temperature associated with membrane release arequite similar to those reported for substrate and pressure variations,suggestive of a common underlying mechanism. These membranes structures shouldprovide a versatile platform for a range of experimental studies and devicesfree from substrate constraints.