Millimeter-scale freestanding superconducting infinite-layer nickelate membranes

TL;DR

This paper presents a method to create freestanding superconducting nickelate membranes, enabling new experimental and device possibilities by removing substrate constraints while maintaining key properties.

Contribution

The authors develop a process to produce millimeter-scale freestanding (Nd,Sr)NiO2 membranes with preserved structural and electronic properties, expanding the toolkit for nickelate research.

Findings

Membranes have similar properties to thin films.

Membranes range from millimeters to ~100 microns.

Superconducting transition temperature changes are consistent with substrate effects.

Abstract

Progress in the study of infinite-layer nickelates has always been highly linked to materials advances. In particular, the recent development of superconductivity via hole-doping was predicated on the controlled synthesis of Ni in a very high oxidation state, and subsequent topotactic reduction to a very low oxidation state, currently limited to epitaxial thin films. Here we demonstrate a process to combine these steps with a heterostructure which includes an epitaxial soluble buffer layer, enabling the release of freestanding membranes of (Nd,Sr)NiO2 encapsulated in SrTiO3, which serves as a protective layer. The membranes have comparable structural and electronic properties to that of optimized thin films, and range in lateral dimensions from millimeters to ~100 micron fragments, depending on the degree of strain released with respect to the initial substrate. The changes in the superconducting transition temperature associated with membrane release are quite similar to those reported for substrate and pressure variations, suggestive of a common underlying mechanism. These membranes structures should provide a versatile platform for a range of experimental studies and devices free from substrate constraints.