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  • Featured in Physics
  • Open Access

Atomic-Scale Tracking of Topological Defect Motion and Incommensurate Charge Order Melting

Noah Schnitzer1, Berit H. Goodge2,3,*, Gregory Powers2, Jaewook Kim4,5, Sang-Wook Cheong4,5, Ismail El Baggari6,7, and Lena F. Kourkoutis2,8

  • *Contact author: Berit.Goodge@cpfs.mpg.de
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Phys. Rev. X 15, 011007 – Published 15 January, 2025

DOI: https://doi.org/10.1103/PhysRevX.15.011007

Abstract

Charge order pervades the phase diagrams of quantum materials where it competes with superconducting and magnetic phases, hosts electronic phase transitions and topological defects, and couples to the lattice generating intricate structural distortions. Incommensurate charge order is readily stabilized in manganese oxides, where it is associated with anomalous electronic and magnetic properties, but its nanoscale structural inhomogeneity complicates precise characterization and understanding of its relationship with competing phases. Leveraging atomic-resolution variable-temperature cryogenic scanning transmission electron microscopy, we characterize the thermal evolution of charge order as it transforms from its ground state in a model manganite system. We find that mobile networks of discommensurations and dislocations generate phase inhomogeneity and induce global incommensurability in an otherwise lattice-locked modulation. Driving the order to melt at high temperatures, the discommensuration density grows, and regions of order locally decouple from the lattice periodicity.

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Orderly State of Electrons Melts on Camera

Published 15 January, 2025

A cryogenic microscope reveals the atomic-scale processes that disrupt the charge-ordered state in a material as the temperature rises.

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Popular Summary

In strongly correlated materials, interactions between electrons give rise to a wide range of exotic properties. Charge order, a periodic pattern of modulated electron density that competes with other phenomena such as superconductivity, has attracted sustained interest due to these interactions and its intriguing coupling to the atomic lattice. In some cases, the charge order periodicity does not match that of the underlying atomic structure. This mismatch results in intricate distortions to atomic structure and other unusual behavior, but in many materials the nature of these incommensurate orderings and how they form remains unclear. We use cryogenic scanning transmission electron microscopy to characterize incommensurate charge order by directly measuring picometer-scale atomic displacements while controlling the sample temperature—the first demonstration combining such temperature control with the necessary high spatial resolution.

We find that while most of the crystal remains static, nanoscale networks of topological defects—points where the order warps—are constantly moving. These defects slightly change the charge order’s periodicity so that it becomes incommensurate with the atomic lattice. The defects multiply as we raise the sample temperature, further disrupting the order and eventually causing it to “melt” entirely (though the crystal itself remains fully intact) at high temperatures. Surprisingly, this melting process decouples parts of the charge order from the periodicity of the atomic lattice, showing that the relationship between charge order and the lattice may be more complex than previously thought.

Looking ahead, this research opens new experimental pathways for exploring how strongly correlated phenomena such as charge order emerge and interact with other phases such as superconductivity and magnetism in quantum materials. Understanding these interactions can help in designing new materials that harness these properties for next-generation technologies.

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Phys. Rev. X 15, 011007– Published 15 January, 2025
  • Received 27 March 2024
  • Revised 8 November 2024
  • Accepted 25 November 2024
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Open access publication funded by the Max Planck Society.

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