Freestanding perovskite and infinite-layer nickelate membranes

TL;DR

This study develops freestanding nickelate membranes using sacrificial layers and investigates their phase stability and transport properties, revealing the importance of a substrate template for stabilizing the infinite-layer phase.

Contribution

We demonstrate a method to fabricate freestanding nickelate membranes and show that a substrate template is essential for stabilizing the infinite-layer phase with desirable properties.

Findings

Membranes transferred from LaAlO$_3$ show better metallic behavior.

Reduction with CaH$_2$ results in insulating characteristics.

A substrate template is crucial for stabilizing the infinite-layer phase.

Abstract

Following the discovery of superconductivity in hole-doped NdNiO$_2$ infinite-layer thin films, extensive research has been conducted particularly to compare these materials with cuprates. Superconductivity has also been observed in nickelate thin films with other rare-earth elements like Pr and La, but not in their bulk forms, suggesting a critical role for substrate-induced strain/interface or dimensionality effects. In this study, we use water-soluble (Ca,Sr)$_3$Al$_2$O$_6$ sacrificial layers to fabricate freestanding perovskite nickelate membranes and explore topotactic reduction without the SrTiO$_3$ substrate as a template. NdNiO$_3$-based heterostructure membranes transferred from a LaAlO$_3$ substrate exhibit better metallic behavior and higher hysteresis than those transferred from SrTiO$_3$, owing to the different strain states that the NdNiO$_3$ layer experience when grown on these two substrates. Despite the expected X-ray diffraction shifts, membranes reduced with CaH$_2$ display insulating characteristics, similar to bulk infinite-layer nickelates. Our findings strongly indicate that a template is necessary to stabilize a coherent and robust infinite-layer phase with optimal transport properties.