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  • Featured in Physics
  • Open Access

More is Less in Unpercolated Active Solids

Jack Binysh1,*, Guido Baardink2, Jonas Veenstra1, Corentin Coulais1,†, and Anton Souslov3,‡

  • *Contact author: j.a.c.binysh@uva.nl
  • †Contact author: coulais@uva.nl
  • ‡Contact author: as3546@cam.ac.uk
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Phys. Rev. X 16, 021012 – Published 13 April, 2026

DOI: https://doi.org/10.1103/flhb-kjyd

Abstract

A remarkable feat of active matter physics is that systems as diverse as collections of self-propelled particles, nematics mixed with molecular motors, and interacting robots can all be described by symmetry-based continuum theories. These descriptions rely on reducing complex effects of individual motors to a few key active parameters, which increase with activity. Here we observe a striking anomaly in the continuum description of nonreciprocal active solids, a ubiquitous class of active materials. Using a combination of metamaterial experiments and coarse-graining theory we find that as microscopic activity increases, macroscale active response can vanish: more is less. In this highly active regime, nonaffine and localized modes prevail and destroy the large-scale signature of microscopic activity. These modes exist in any dilute periodic structure and emerge in random lattices below a percolation transition. Our results unveil a counterintuitive facet of active matter, offering new principles for engineering materials far from equilibrium.

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Physics Subject Headings (PhySH)

Viewpoint

In Active Solids, Connectivity Is as Important as Activity

Published 13 April, 2026

A robotic metamaterial shows that the odd mechanics of active solids depend on how the active constituents connect across the system.

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Popular Summary

It is often intuitively assumed that stiffening a material’s building blocks leads to a stiffer overall structure. We demonstrate a breakdown of this principle in robotic metamaterials, where increasing microscopic activity can cause the macroscale active response to vanish. Through experiments and theory, we find that this anomaly is due to the arrangement of active units within the solid. If the robots are too far apart, their locally exerted forces cannot percolate through the whole material. We lay out the rules for how this percolation transition occurs, and show that, in underpercolated lattices, activity becomes trapped in localized vibrations and does not lead to a collective response. Our results establish design principles for active solids, with applications ranging from soft matter and biophysics to driven quantum materials.

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Phys. Rev. X 16, 021012– Published 13 April, 2026
  • Received 25 April 2025
  • Accepted 5 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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