{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"4728dfe5f4a9916ae960cbd96373d61f09d01aec8dd1026bb86fd9b88855add2","created":"2026-10-03T07:18:00Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"b8ec77e39735ed5a0316e1ef7a0e721bf6bfd6a8384ccd9834198ec2dce1e125","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"classification","assisted_by":[],"external_id":"cm.hubbard-mott.mott-endpoint-universality","kind":"well-posed","literature_status":"contested","n":"1","parents":[],"plain":"Squeezing certain organic salts turns them from Mott insulators into metals through a jump, like liquid turning into gas, that ends at a critical point; the measured critical exponents disagree with the liquid-gas prediction.","posed_since":"2005","precise":"In kappa-(BEDT-TTF)2Cu[N(CN)2]Cl the first-order Mott metal-insulator line ends at a critical point near $T_{\\mathrm{cr}} \\sim 40\\ \\mathrm{K}$ and $P_{\\mathrm{cr}} \\sim 250\\ \\mathrm{bar}$. Conductivity scaling (Kagawa, Miyagawa, Kanoda, Nature 2005) gave $\\beta \\sim 1$ and $\\delta \\sim 2$, far from 3D Ising values ($\\beta \\sim 0.33,\\ \\delta \\sim 4.8$) and from 2D Ising ($\\beta = 1/8,\\ \\delta = 15$). Determine the universality class of the endpoint and how conductivity couples to the scaling fields (order parameter and energy density). An answer is a set of thermodynamic exponents (thermal expansion, compressibility, specific heat) measured at the endpoint, plus a theory of conductivity scaling consistent with them.","problem_ref":null,"references":"","settled_by":"Thermodynamic critical exponents measured near $T_{\\mathrm{cr}}$ with pressure resolution sufficient to separate Ising classes, together with a model that maps the scaling fields onto the measured conductivity exponents.","status_note":"Furukawa et al. (Nature Physics 2015) reported quantum-critical scaling of resistivity across the high-temperature Mott crossover; the class of the finite-temperature endpoint is still unsettled.","title":"Universality class of the Mott critical endpoint in organic 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