The layered cobaltate CaCoO2 exhibits a unique herringbone-like structure. Serving as a potential prototype for a new class of complex lattice patterns, we study the properties of CaCoO2 using X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS). Our results reveal a significant inter-plane hybridization between the Ca 4s− and Co 3d−orbitals, leading to an inversion of the textbook orbital occupation of a square planar geometry. Further, our RIXS data reveal a strong low energy mode, with anomalous intensity modulations as a function of momentum transfer close to a quasi-static response suggestive of electronic and/or orbital ordering. These findings indicate that the newly discovered herringbone structure exhibited in CaCoO2 may serve as a promising laboratory for the design of materials having strong electronic, orbital and lattice correlations.
@article{arxiv.2409.07705,
title = {Orbital inversion and emergent lattice dynamics in infinite layer CaCoO$_2$},
author = {Daniel Jost and Eder G. Lomeli and Woo Jin Kim and Emily M. Been and Matteo Rossi and Stefano Agrestini and Kejin Zhou and Chunjing Jia and Brian Moritz and Zhi-Xun Shen and Harold Y. Hwang and Thomas P. Devereaux and Wei-Sheng Lee},
journal= {arXiv preprint arXiv:2409.07705},
year = {2026}
}