{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"5bc898d2c92289690981cb6bb5e2508879c1a23fad1a342ce4ac81db0f694f29","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["c2731729d4b609c42a63ef14bfdffea0ca9236413ca2b0e8ba77172a87e5e0cf","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"dbeb44b6cda7d192714c4c739921f1419663466727e8bcf9c780a797726c88b7","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"identification","assisted_by":[],"external_id":"cm.cuprate-pseudogap.oscillation-pockets","kind":"well-posed","literature_status":"partially-resolved","n":"2","parents":[],"plain":"In strong magnetic fields, underdoped YBa2Cu3O6+x shows quantum oscillations, field-periodic wiggles in resistance that reveal a small closed pocket of electrons, whereas at zero field the Fermi surface is a single large hole-like contour; some order must cut the large surface into pieces.","posed_since":"2007","precise":"In YBa2Cu3O6+x ($p \\sim 0.08\\ \\text{to}\\ 0.15$) and HgBa2CuO4+d with superconductivity suppressed by $300\\ \\text{to}\\ 900\\,\\mathrm{kG}$, quantum oscillations show a dominant frequency $F \\sim 5.3\\,\\mathrm{MG}$ (about 2 percent of the Brillouin zone) and a negative Hall coefficient, indicating an electron pocket. Determine whether biaxial charge order with the measured $q_{\\mathrm{CDW}}$ alone reconstructs the Fermi surface into this electron pocket, and where the additional hole pockets required by Luttinger counting are, or why they are absent. An answer is a reconstruction model reproducing F, its splitting and c-axis warping, the Hall sign and the carrier count, together with detection or exclusion of the predicted extra pockets.","problem_ref":"c2731729d4b609c42a63ef14bfdffea0ca9236413ca2b0e8ba77172a87e5e0cf","references":"","settled_by":"Quantum-oscillation detection, or a bound on the amplitude, of the predicted hole pockets in the same field and doping range, plus angle-resolved oscillation data matching the proposed reconstruction.","status_note":"Reconstruction by charge order is the leading explanation of the electron pocket, but the hole pockets that such reconstructions predict have not been observed.","title":"What reconstructs the underdoped cuprate Fermi surface into small 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