A single crystal sample of the spin-1/2 kagome quantum spin liquid candidate herbertsmithite. Credit: Lee group, Stanford University.

Quantum spin liquids are exotic states of matter in which spins (i.e., the intrinsic angular momentum of electrons) do not settle into an ordered pattern and continue to fluctuate, even at extremely low temperatures. This state is characterized by high entanglement, a quantum effect that causes particles to become linked so that the state of one affects the others’ states, even over long distances.

Researchers at SLAC National Accelerator Laboratory and Stanford University recently gathered evidence of intrinsic quantum spin liquid behavior in a kagome material, a magnetic material in which atoms are arranged in a particular pattern known as a kagome lattice. Their findings, published in Nature Physics, could help to further delineate the fundamental principles underpinning quantum spin liquid states.

"I’ve been interested in understanding quantum spin liquids for the past 20+ years," Young S. Lee, senior author of the paper, told Phys.org. "These are fascinating new states of quantum matter. In principle, their ground states may possess long-range quantum entanglement, which is extremely rare in real materials.

"My group has synthesized single crystal samples of candidate quantum spin liquid (QSL) candidates, as crystals are essential for detailed measurements of the spin excitations using powerful neutron scattering techniques."

Single crystal samples of the spin-1/2 kagome quantum spin liquid candidate Zn-barlowite Credit: Lee group, Stanford University.

As part of their earlier works, Lee and his colleagues gathered observations that hinted at the presence of exotic excitations in the spin-1/2 kagome material herbertsmithite. The excitations they reported were assumed to be a strong signature of quantum spin liquid states.

"One could question whether these prior results are generally applicable to the QSL state or are rather just unique to the material being studied," said Lee. "In this paper, we made crystals of the new kagome QSL material Zn-barlowite to perform experiments to resolve this question."

Probing quantum states in kagome magnets

Building on their previous observations, Lee and his colleagues set out to examine a new magnetic material with a kagome lattice, known as Zn-barlowite. Firstly, they synthesized high-quality samples of the material and cooled them to very low temperatures, where they could probe its ground (i.e., lowest-energy) state.

They then used a technique known as high-resolution inelastic neutron scattering, which can be used to study how spins absorb and release energy, to measure excitations in single Zn-barlowite crystals. Finally, they compared their observations with the theoretical predictions derived using a numerical approach known as the density matrix renormalization group (DMRG).

"Neutrons can penetrate deep inside the materials and scatter from the spin-1/2 moments in the active kagome layers," explained Lee.

"The scattering pattern gives us two important pieces of microscopic information. The first is how the spin directions are correlated in space and the second is how they fluctuate in time. These measurements revealed that the fundamental excitations of the kagome spins appear in the form of ‘spinons’ which are fractionalized pieces of typical ‘magnon’ excitations."

Universal quantum spin liquid behavior in kagome materials

The exotic behavior that the team observed in Zn-barlowite was aligned with the excitations that they previously observed in herbertsmithite. Therefore, their study suggests that the same quantum spin liquid state is universally present in many known kagome materials.

"A long-sought goal in the field is to achieve consensus on at least one real material (or family of related materials) that has irrefutable evidence for a QSL ground state," said Lee.

"This would entail having detailed experimental data which match corresponding theoretical predictions specifically related to that material. Our work in this paper, supported by SLAC National Accelerator Laboratory, reports detailed information on the spin correlations that match well with theoretical calculations for a particular QSL ground state. I think our results are a further important step towards this overall goal."

The new results published by Lee and his colleagues could soon contribute to the understanding of quantum spin liquid states and their unique signatures. In the future, a better grasp of these states could potentially inform the development of promising new quantum technologies.

"Once quantum spin liquids are verified in real materials, one can hope that their exotic quantum entanglement properties can be exploited for applications in areas such as in quantum information storage or quantum computation," added Lee.

"Yet at the moment, I am still engrossed in understanding the fundamental physics of these quantum magnets. Experimental probes of quantum entanglement are currently lacking. It would be fascinating to explore new ways to characterize the quantum entanglement in our materials with indirect means and hopefully find more direct means."

Written for you by our author Ingrid Fadelli, edited by Gaby Clark, and fact-checked and reviewed by Robert Egan—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive. If this reporting matters to you, please consider a donation (especially monthly). You’ll get an ad-free account as a thank-you.

More information: Aaron T. Breidenbach et al, Identifying universal spin excitations in candidate spin-1/2 kagome quantum spin liquid materials, Nature Physics (2025). DOI: 10.1038/s41567-025-03069-3. On arXiv: DOI: 10.48550/arxiv.2504.06491

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Citation: Evidence of a quantum spin liquid ground state in a kagome material (2025, December 27) retrieved 27 December 2025 from https://phys.org/news/2025-12-evidence-quantum-liquid-ground-state.html

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