{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"8415cf9e9dbc59669105237e1a261bcb0d0370a188235702736a434326bc2012","created":"2026-10-03T07:18:01Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"f39754bd0de4561450bfa6b69efb5b3ae4a2c066cb3cd358fff308fd962531bc","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"identification","assisted_by":[],"external_id":"cm.triangular-kagome-spin-liquids.spinon-fermi-surface","kind":"phenomenon","literature_status":"open","n":"1","parents":[],"plain":"A spinon Fermi surface would make an electrical insulator behave like a metal for spin and heat. Candidates include organic triangular-lattice salts and the layered compound 1T-TaS2, but no measurement has established it.","posed_since":"2005","precise":"Identify an insulating magnet in a $U(1)$ spin-liquid state with a spinon Fermi surface, signaled by a magnetic specific heat $C \\sim T^{2/3}$ (or $C/T \\to \\mathrm{const}$ if gauge fluctuations are weak) and a magnetic $\\kappa/T \\to \\mathrm{const}$ as $T \\to 0$, plus $2k_F$ singularities in the spin structure factor or quantum oscillations of a neutral Fermi surface. An answer is a material with at least two independent such signatures reproduced across samples, or a demonstration that all present candidates have other ground states.","problem_ref":null,"references":"","settled_by":"Combined low-temperature heat capacity, thermal conductivity and spectroscopic evidence on one material, reproduced by independent groups.","status_note":"A residual $\\kappa_{0}/T > 0$ in EtMe3Sb[Pd(dmit)2]2 (Yamashita et al., Science 2010) was not reproduced by Ni et al. (PRL 2019) or Bourgeois-Hope et al. (PRX 2019); no candidate has two reproduced signatures.","title":"Does any insulator host a spinon Fermi 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