Observation of an emergent energy scale close to dimensional reduction in a quasi-two-dimensional quantum magnet

Anneke Reinold; Laur Peedu; Kirill Amelin; Urmas Nagel; Toomas Rõõm; Sven Luther; Hannes Kühne; Dirk Wulferding; Kingshuk Mukhuti; Maarten W. de Dreu; Peter C. M. Christianen; Dennis Kudlacik; Dmitri Yakovlev; Zhiying Zhao; Taro Nakajima; Yoshimitsu Kohama; Thomas Lorenz; Franco Lisandrini; Corinna Kollath; Marcin Raczkowski; Fakher F. Assaad; Zhe Wang

arXiv · 2607.23547

Observation of an emergent energy scale close to dimensional reduction in a quasi-two-dimensional quantum magnet

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Abstract

By appropriately perturbing a critical transverse-field Ising chain away from its critical point, the system can develop a finite correlation length with a characteristic purely massive spectrum, whose ratios and correlations are precisely described by an integrable field theory and an infinite set of integrals of motion corresponding to the $E_8$ Lie algebra. In this work, we report on experimental observation of a characteristic massive spectrum close to transverse field-induced dimensional reduction in a quasi-two-dimensional quantum magnet Cu$_2$(OH)$_3$Br, providing evidence for an emergent $E_8$ symmetry and the corresponding excitations of bound states in the sublattice of its ferromagnetic chains. These results demonstrate the power of integrable field theory in describing emergent many-body quantum critical phenomena in condensed matter systems.

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Anneke Reinold, Laur Peedu, Kirill Amelin, Urmas Nagel, Toomas Rõõm, Sven Luther, Hannes Kühne, Dirk Wulferding, Kingshuk Mukhuti, Maarten W. de Dreu, Peter C. M. Christianen, Dennis Kudlacik, Dmitri Yakovlev, Zhiying Zhao, Taro Nakajima, Yoshimitsu Kohama, Thomas Lorenz, Franco Lisandrini, Corinna Kollath, Marcin Raczkowski, Fakher F. Assaad, Zhe Wang. 2026-07-26. Observation of an emergent energy scale close to dimensional reduction in a quasi-two-dimensional quantum magnet. https://arxiv.org/abs/2607.23547

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