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arXiv · 2409.07705

Orbital inversion and emergent lattice dynamics in infinite layer CaCoO$_2$

Daniel Jost·Eder G. Lomeli·Woo Jin Kim·Emily M. Been·Matteo Rossi·Stefano Agrestini·Kejin Zhou·Chunjing Jia·Brian Moritz·Zhi-Xun Shen·Harold Y. Hwang·Thomas P. Devereaux·Wei-Sheng Lee
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Abstract

The layered cobaltate CaCoO$_2$ exhibits a unique herringbone-like structure. Serving as a potential prototype for a new class of complex lattice patterns, we study the properties of CaCoO$_2$ 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 CaCoO$_2$ may serve as a promising laboratory for the design of materials having strong electronic, orbital and lattice correlations.

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Daniel Jost, Eder G. Lomeli, Woo Jin Kim, Emily M. Been, Matteo Rossi, Stefano Agrestini, Kejin Zhou, Chunjing Jia, Brian Moritz, Zhi-Xun Shen, Harold Y. Hwang, Thomas P. Devereaux, Wei-Sheng Lee. 2024-09-12. Orbital inversion and emergent lattice dynamics in infinite layer CaCoO$_2$. https://doi.org/10.1038/s41535-025-00778-z

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