{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"82d9d7041ec86e003dfc383ac530b0020dd2f668304455aaeaacdc6bb65d0c86","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":["ai:gpt-5.5"],"kind":"seed"},"parents":["ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b","f282a8930978eb748e2f875a7c24ea2da93a36b7f78757e6b7832deb0faf0f08"],"salt":"d0cc93e225a7c6dc07b6040482544b65306d9da1c11a948f6b7ec0b20f8f4daf","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"classification","assisted_by":["ai:gpt-5.5"],"external_id":"cm.spin-ice.pi-flux-classification","kind":"well-posed","literature_status":"contested","n":"2","parents":[],"plain":"Quantum spin ice comes in two versions, labeled zero-flux and pi-flux, that differ in how emergent charges feel the internal magnetic field. Which version each cerium compound realizes depends on the signs of its exchange couplings, which are still debated.","posed_since":"","precise":"For $\\mathrm{Ce_2Zr_2O_7}$, $\\mathrm{Ce_2Sn_2O_7}$ and $\\mathrm{Ce_2Hf_2O_7}$ described by the dipolar-octupolar Hamiltonian H = sum_<ij> [J_x tau^x_i tau^x_j + J_y tau^y_i tau^y_j + J_z tau^z_i tau^z_j + J_xz (tau^x_i tau^z_j + tau^z_i tau^x_j)], determine the exchange parameters and the sign of the dominant transverse coupling that fixes the zero-flux or $\\pi$-flux $U(1)$ phase, and confirm it by the predicted spinon-continuum structure. An answer is the classification per compound with fitted parameters.","problem_ref":"f282a8930978eb748e2f875a7c24ea2da93a36b7f78757e6b7832deb0faf0f08","references":"","settled_by":"Global fits of neutron spectra, heat capacity and magnetization in field to the XYZ model, compared with the distinct spinon spectra of each flux phase.","status_note":"Gao et al. (2025) classify $\\mathrm{Ce_2Zr_2O_7}$ as $\\pi$-flux; parameter fits differ across groups and compounds.","title":"Zero-flux or pi-flux quantum spin ice in cerium 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