Two acoustic experiments find topological signatures at gapless critical points
Separate studies in Nature report topological features at phase boundaries in engineered acoustic systems, challenging a conventional divide in how phase transitions are described.
Two studies published in Nature on October 7, 2026, report experimental evidence that topological features can persist at gapless critical points. Teams led by Baile Zhang at Nanyang Technological University in Singapore and Jian-Hua Jiang at the University of Science and Technology of China used engineered acoustic systems to examine phase boundaries that have been difficult to describe using conventional topological measures. The results matter because they offer laboratory evidence for a connection between topology and critical behavior, while leaving its use in quantum materials or devices open.
The studies are separate experiments, with different author teams and methods. Both include Xue-Jia Yu of the Eastern Institute of Technology, Ningbo, as an author; an account supplied by that institute describes Yu as a co-corresponding author on both papers. Their shared subject is whether meaningful topological distinctions survive when a system reaches a gapless phase boundary.
Why a gapless phase boundary matters
The question joins two established ways of understanding phases of matter. Conventional continuous transitions occur at critical points with gapless fluctuations and behavior that can look similar across otherwise different systems. Topological phases, by contrast, are usually distinguished by quantized properties defined for gapped systems. At a boundary where the gap closes, the familiar invariant may cease to be well defined. That has made criticality and topology appear difficult to describe together, even though earlier theory had explored their possible connection.
Neither paper presents the idea of critical topology as emerging without precedent. Both place their experiments against earlier theoretical and experimental research. The new contribution they report is evidence from constructed systems: measurements of boundary behavior and other signatures at critical points, interpreted through the frameworks developed for topological phases and phase transitions.
What the phononic-crystal experiment found
In ‘Experimental observation of critical topology,’ the team associated with Jiang reports evidence for critical gapless topological states in one and two dimensions using engineered phononic crystals. The authors say they characterized these states with entanglement spectra and entanglement wavefunctions and directly imaged topological boundary modes within a gapless bulk continuum. These are reported experimental signatures in a designed acoustic setting, rather than observations of a naturally occurring quantum material.
The same paper describes transitions between phase boundaries with distinct critical topology. Its authors interpret those transitions as producing multicritical points and a hierarchy of topological phases. In that account, topology can help organize what happens along critical boundaries, instead of serving only to distinguish phases on either side of a boundary. That interpretation is part of the paper’s reported result and rests on its entanglement-based analysis and boundary-mode measurements.
What the acoustic metamaterial experiment found
In ‘Observation of critical topological phase transition,’ the team associated with Zhang used an acoustic metamaterial to investigate a transition along critical phase boundaries. The authors report topological edge states on those boundaries and use logarithmic scaling of entanglement entropy to diagnose critical behavior. Their measurements therefore address both parts of the claim: a topological signature at an edge and evidence that the system is at criticality.
The Zhang team also reports an isolated intersection of critical boundaries with different topology. At that point, the measured entanglement entropy showed additive logarithmic scaling, which the authors interpret as evidence of topology-enforced multicriticality. This is a more specific claim than simply finding an edge state: it proposes that topological distinctions can shape the organization of critical points themselves. The paper describes an acoustic implementation of the experiment, including measurements around 9.8 kilohertz.
What remains to be tested in quantum systems
The distinction between the platforms and possible applications is central to both reports. The phononic-crystal paper explicitly describes its implementation as classical. Its authors say the approach gives results equivalent to those in the quantum limit and could be extended to quantum systems, but they do not report having demonstrated it in one. The acoustic metamaterial experiment likewise establishes its reported signatures on an engineered acoustic platform.
The papers advance the experimental study of topology at phase transitions. They do not establish that the same methods will work in a practical quantum device, or that the observed critical states will yield a usable technology. Further work would have to test how the measurements and interpretations carry over to quantum systems. For now, the published result is narrower and concrete: two teams report distinct laboratory routes to observing topological behavior where the conventional energy-gap picture presents a challenge.
Sources and context
- Experimental observation of critical topologyNature
- Observation of critical topological phase transitionNature
- Acoustic experiments confirm topology can persist at gapless critical pointsPhys.org (article provided by Eastern Institute of Technology, Ningbo)
AI-assisted article checked against the listed sources. NewsJaws did not conduct interviews or attend the reported events.
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