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 PrNiO2 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.
@article{arxiv.2404.17795,
title = {Discovery of Giant Unit-Cell Super-Structure in the Infinite-Layer Nickelate PrNiO$_2$},
author = {J. Oppliger and J. Küspert and A. -C. Dippel and M. v. Zimmermann and O. Gutowski and X. Ren and X. J. Zhou and Z. Zhu and R. Frison and Q. Wang and L. Martinelli and I. Biało and J. Chang},
journal= {arXiv preprint arXiv:2404.17795},
year = {2025}
}