{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"ef7b12e33e3211d28818919631027abbc1761ac9c458eab722b4ee067d4f6c93","created":"2026-10-03T07:18:01Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"3ce3f077fb913aaa8629ddcb9b63faf51977449b15ad51153841c61ee4e15db4","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":[],"external_id":"cm.triangular-kagome-spin-liquids.herbertsmithite-spin-gap","kind":"phenomenon","literature_status":"contested","n":"1","parents":[],"plain":"Herbertsmithite, ZnCu3(OH)6Cl2, is the best-studied kagome spin-liquid material, but some copper and zinc atoms swap places. Nuclear magnetic resonance experiments disagree with each other on whether there is a small energy gap, and the defects make the data hard to interpret.","posed_since":"","precise":"In ZnCu3(OH)6Cl2 ($J/k_B$ about 190 K), determine whether the kagome-plane spin excitations have a gap $\\Delta > 0$ as $T \\to 0$ once the contribution of Cu on interlayer Zn sites (about 5 to 15 percent) is subtracted. An answer is $\\Delta/J$ with uncertainty, or an upper bound consistent with zero, reconciled across NMR, neutron and thermodynamic data.","problem_ref":null,"references":"","settled_by":"Site-selective NMR and polarized neutron spectroscopy on crystals with independently measured defect content, analyzed with a model including the interlayer Cu spins.","status_note":"17O NMR by Fu et al. (Science 2015) reported a gap of a few percent of J, while later 17O NMR by Khuntia et al. (Nature Physics 2020) and neutron data indicate a gapless state; the role of interlayer Cu defects remains debated.","title":"Does herbertsmithite have an intrinsic spin 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