Gapped magnetic ground state in quantum spin liquid candidate κ-(BEDT-TTF) 2 Cu 2 (CN) 3

Geometrical frustration, quantum entanglement, and disorder may prevent long-range ordering of localized spins with strong exchange interactions, resulting in an exotic state of matter. κ-(BEDT-TTF) Cu (CN) is considered the prime candidate for this elusive quantum spin liquid state, but its ground-...

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Bibliographic Details
Published in:Science (American Association for the Advancement of Science) 2021-04, Vol.372 (6539), p.276-279
Main Authors: Miksch, Björn, Pustogow, Andrej, Rahim, Mojtaba Javaheri, Bardin, Andrey A, Kanoda, Kazushi, Schlueter, John A, Hübner, Ralph, Scheffler, Marc, Dressel, Martin
Format: Article
Language:English
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Summary:Geometrical frustration, quantum entanglement, and disorder may prevent long-range ordering of localized spins with strong exchange interactions, resulting in an exotic state of matter. κ-(BEDT-TTF) Cu (CN) is considered the prime candidate for this elusive quantum spin liquid state, but its ground-state properties remain puzzling. We present a multifrequency electron spin resonance (ESR) study down to millikelvin temperatures, revealing a rapid drop of the spin susceptibility at 6 kelvin. This opening of a spin gap, accompanied by structural modifications, is consistent with the formation of a valence bond solid ground state. We identify an impurity contribution to the ESR response that becomes dominant when the intrinsic spins form singlets. Probing the electrons directly manifests the pivotal role of defects for the low-energy properties of quantum spin systems without magnetic order.
ISSN:0036-8075
1095-9203
DOI:10.1126/science.abc6363