{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"4609c31a15fb5b5d0d66ccaddd639adcc2f8eca398600168b1612180c5fe789c","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["b3a2b4f7e2cc646c0fa3d74d645e3e321a0a0842e50635e3da3e2c2840f55d81","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"4c8b7c92b39d7f68eb607e0f2b16f202af41e0a55cc628187d2ecb076f533604","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"identification","assisted_by":[],"external_id":"cm.nickelates.bulk-sc-polymorph","kind":"well-posed","literature_status":"partially-resolved","n":"2","parents":[],"plain":"Early pressure experiments found only a small superconducting volume, and $\\mathrm{La_3Ni_2O_7}$ crystals contain two stacking patterns of nickel-oxide layers, so which structure superconducts in bulk was unclear.","posed_since":"2023","precise":"Determine which structural polymorph of $\\mathrm{La_3Ni_2O_7}$ at high pressure (bilayer 2222 or alternating monolayer-trilayer 1313) carries the $\\sim 80\\,\\mathrm{K}$ superconductivity, and whether the superconducting volume fraction in phase-pure stoichiometric crystals is bulk. An answer combines diffraction under pressure with ac susceptibility volume fractions on the same phase-pure samples.","problem_ref":"b3a2b4f7e2cc646c0fa3d74d645e3e321a0a0842e50635e3da3e2c2840f55d81","references":"","settled_by":"Shielding-fraction measurements near 100 percent on phase-pure samples of each polymorph with simultaneous structural determination.","status_note":"Bulk superconductivity was reported in $\\mathrm{La_2PrNi_2O_7}$ under pressure (2024) and in pressurized bilayer nickelate crystals up to about $96\\,\\mathrm{K}$ (2025), and superconductivity was also reported in the 1313 polymorph (2025).","title":"Which $\\mathrm{La_3Ni_2O_7}$ polymorph carries bulk superconductivity under 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