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  • Letter
  • Open Access

Observing octupolar charge orders and their transition dynamics in Coulomb clusters

Akhil Ayyadevara1,*, Anand Prakash1, Shovan Dutta1, Arun Paramekanti2, and S. A. Rangwala1

  • *Contact author: akhilv@rri.res.in
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Phys. Rev. Research 8, L012066 – Published 18 March, 2026

DOI: https://doi.org/10.1103/2rs1-c5r1

Abstract

Interacting many-particle systems can self-organize into a rich variety of crystalline structures. While symmetry provides a powerful framework for predicting whether transitions between crystal states are continuous or discontinuous, collective lattice dynamics offer complementary insights into the microscopic mechanisms that drive these transitions. Trapped laser-cooled ions present a pristine and highly controllable system for studying this interplay of symmetry and dynamics. Here, we use real-time fluorescence imaging while deforming the trap potential to observe a variety of structural transitions in three-dimensional (3D), unit-cell-like ion clusters. We identify a set of unexplored transitions signaled by parity-odd octupole order parameters and probe their distinct dynamical signatures. Our experiments reveal the softening of a collective Higgs-like mode, indicating spontaneous symmetry breaking, hysteresis resulting from a catastrophe where a metastable state vanishes abruptly, and stochastic switching between metastable states of distinct symmetries. We also uncover a remarkable coincidence of symmetry-breaking and discontinuous transitions, analogous to a thermodynamic triple point. Our results establish 3D trapped-ion clusters as a versatile platform for engineering complex potential energy landscapes, opening avenues for studying collective phenomena such as geometric frustration with multipolar orders and the stochastic kinetics of rare events in exotic mesoscopic settings.

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Phys. Rev. Research 8, L012066– Published 18 March, 2026
  • Received 17 October 2025
  • Accepted 9 February 2026
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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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