Cooperative Charge Ordering Signature of Trimer Molecules in Infinite-Layer CaCoO₂

Authors

• J. S. Lee, Stanford Synchrotron Radiation LightsourceFollow
• W. J. Kim, Stanford University
• A. Khandelwal, Stanford University
• K. T. Ko, Korea Basic Science Institute
• H. Lee, Stanford Synchrotron Radiation Lightsource
• C. T. Kuo, Stanford Synchrotron Radiation Lightsource
• S. Song, Stanford Linear Accelerator Center
• C. Song, Pohang University of Science and Technology
• D. Jang, Pohang University of Science and Technology
• H. Choi, Pohang Accelerator Laboratory
• G. Park, Pohang Accelerator Laboratory
• S. Y. Park, Pohang Accelerator Laboratory
• G. Kang, Pohang Accelerator Laboratory
• H. Jang, University of Kentucky
• P. Abdollahi, University of Kentucky
• A. Seo, University of Kentucky
• C. C. Kao, Stanford Synchrotron Radiation Lightsource
• H. Y. Hwang, Stanford UniversityFollow

Abstract

The infinite-layer compound CaCoO₂ provides a compelling platform to explore how local orbital distortions evolve into collective electronic order. Using resonant soft x-ray scattering (RSXS) and its time-resolved counterpart (tr-RSXS), we reveal a cooperative coupling between two intertwined orders at the same in-plane wave vector, q≈(1/4,1/4,0), comprising a quasi-two-dimensional orbital order associated with the distorted Co(1) sites and a quasi-three-dimensional trimerlike charge order stabilized through Co-O-Ca hybridization. The charge-sensitive component exhibits a uniform relaxation time of ∼400 fs (391±5 fs) across multiple Co resonances, evidencing a collective charge response. A comparable timescale observed in the orbital order associated with the highly distorted Co(1) sites indicates that this collective behavior naturally originates from the same orbital framework that mediates both charge and orbital degrees of freedom. Together, these findings establish CaCoO₂ as a model system in which Jahn-Teller distortions, orbital hybridization, and geometric frustration cooperate to form molecular trimer units that dictate the macroscopic electronic behavior.

Document Type

Article

Publication Date

1-1-2026

Notes/Citation Information

Publisher Copyright: © 2026 authors. Published by the American Physical Society.

Digital Object Identifier (DOI)

10.1103/scdr-tmq4

Archival?

Archival

Repository Citation

Lee, J. S.; Kim, W. J.; Khandelwal, A.; Ko, K. T.; Lee, H.; Kuo, C. T.; Song, S.; Song, C.; Jang, D.; Choi, H.; Park, G.; Park, S. Y.; Kang, G.; Jang, H.; Abdollahi, P.; Seo, A.; Kao, C. C.; and Hwang, H. Y., "Cooperative Charge Ordering Signature of Trimer Molecules in Infinite-Layer CaCoO₂" (2026). Physics and Astronomy Faculty Publications. 797.
https://uknowledge.uky.edu/physastron_facpub/797