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Spatial Correlations of Charge Density Wave Order across the Transition in 2H−NbSe2

Seokjo Hong1,*, Jaewhan Oh1,*, Jemin Park1,*, Woohyun Cho1, Soyoung Lee1, Colin Ophus2, Yeongkwan Kim1,†, Heejun Yang1,3,‡, SungBin Lee1,§ et al.

Yongsoo Yang1,3,∥

  • *These authors contributed equally to this work.
  • †Contact author: yeongkwan@kaist.ac.kr
  • ‡Contact author: h.yang@kaist.ac.kr
  • §Contact author: sungbin@kaist.ac.kr
  • ∥Contact author: yongsoo.yang@kaist.ac.kr
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Phys. Rev. Lett. 136, 016504 – Published 6 January, 2026

DOI: https://doi.org/10.1103/776d-dnmf

Abstract

Charge density waves (CDWs) involve coupled amplitude and phase degrees of freedom, but direct access to local amplitude correlations remains experimentally challenging. Here, we report cryogenic four-dimensional scanning transmission electron microscopy measurements of CDW ordering in a 2H−NbSe2 flake of 24 nm thickness, enabled by liquid-helium-based cooling. By mapping the spatial distribution of CDW superlattice intensities at nanometer-scale resolution and analyzing their autocorrelations, we extract the temperature-dependent correlation length associated with the local amplitude of the CDW order parameter, independent of global phase coherence. Our results reveal that a finite local CDW amplitude is already established well above the transition temperature. When the system is cooled below the transition temperature down to 20 K, the correlation length extends to nearly 110 nm, and the local CDW amplitude is found to strongly anticorrelate with the local strain field.

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Phys. Rev. Lett. 136, 016504– Published 6 January, 2026
  • Received 3 June 2025
  • Revised 27 November 2025
  • Accepted 2 December 2025
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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.

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