Discovery of Giant Unit-Cell Super-Structure in the Infinite-Layer Nickelate PrNiO$_2$

TL;DR

This study reveals a giant superlattice structure in PrNiO$_2$ induced by temperature annealing, which may influence its electronic properties and offers a new approach to flat-band physics and ultra-small Brillouin zone electronics.

Contribution

It demonstrates the formation of a giant unit-cell superstructure in PrNiO$_2$ through in-situ annealing, highlighting a novel pathway for engineering flat-band systems.

Findings

Giant superlattice structure observed after annealing

Period-six in-plane and period-four out-of-plane symmetries identified

Superstructure likely due to oxygen ordering

Abstract

Spectacular quantum phenomena such as superconductivity often emerge in flat-band systems where Coulomb interactions overpower electron kinetics. Engineering strategies for flat-band physics is therefore of great importance. Here, using high-energy grazing-incidence x-ray diffraction, we demonstrate how in-situ temperature annealing of the infinite-layer nickelate PrNiO$_2$ induces a giant superlattice structure. The annealing effect has a maximum well above room temperature. By covering a large scattering volume, we show a rare period-six in-plane (bi-axial) symmetry and a period-four symmetry in the out-of-plane direction. This giant unit-cell superstructure likely stems from ordering of diffusive oxygen. The stability of this superlattice structure suggests a connection to an energetically favorable electronic state of matter. As such, our study provides a new pathway - different from Moir\'e structures - to ultra-small Brillouin zone electronics.