Spinon mediation of witness spin dynamics in herbertsmithite

Takahashi, Hiroto, Murphy, Jack, Wood-Thanan, Mitikorn, Puphal, Pascal, Sánchez-Martínez, Miguel-Ángel, Jerzembeck, Fabian, Hsu, Chun-Chih, Ward, Jonathan, Isobe, Masahiko, Matsumoto, Yosuke, Takagi, Hidenori, Blundell, Stephen J., Norman, Michael R., Flicker, Felix and Davis, J. C. Séamus 2026. Spinon mediation of witness spin dynamics in herbertsmithite. Nature Physics 22 , pp. 1071-1078. 10.1038/s41567-026-03303-6

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Abstract

The kagome lattice of spin-1/2 copper atoms in herbertsmithite is conjectured to sustain a quantum spin liquid state with spinon quasiparticles. Ideally, the kagome crystal planes are each separated by a plane of spinless zinc atoms. However, in real crystals, some spin-1/2 copper atoms substitute randomly onto these inter-kagome zinc sites. Here we reconceptualize such ‘impurity’ atoms as quantum witness spins whose dynamics is designed to probe the spin liquid state. We then introduce spin noise spectroscopy to measure the frequency and temperature dependence of witness spin dynamics, demonstrating that their phenomenology is consistent with extensive interactions between witness spins mediated by propagation of spinons through a quantum spin liquid. Ultimately, a sharp transition occurs at around 260 mK, below which the properties of both spin noise and magnetic susceptibility suggest that the witness spins form a spin glass phase. Among the theoretical models considered, we demonstrate that our observations are only consistent with spinon-mediated interactions between witness spins by either a Z2 or U(1) quantum spin liquid, with the former model more closely matching the data. Our work demonstrates that quantum mechanical witness spins may now conceivably be used as a widely applicable probe of quantum spin liquid physics.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Schools > Physics and Astronomy
Publisher:	Nature Research
ISSN:	1745-2473
Date of First Compliant Deposit:	22 June 2026
Date of Acceptance:	17 April 2026
Last Modified:	02 Sep 2026 14:17
URI:	https://orca.cardiff.ac.uk/id/eprint/187676

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