{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"7afcc5bb6e7eae0d7aab4efa32f5efa84f97b168795950455d84976207751c0f","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["cdeabbeea29a0e0a73646cc5ad97161b617805327ba35f4e49f91a7f93c949de","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"ed63c3d6ae323754d8c5b329484a7494ec9e02022bcef4d054adb6bc00b82f26","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"mechanism","assisted_by":[],"external_id":"cm.phonon-thermal-hall.ubiquity-mechanism","kind":"phenomenon","literature_status":"contested","n":"2","parents":[],"plain":"Sideways heat flow in a magnetic field appears in magnetic and non-magnetic insulators alike, with roughly similar size relative to the ordinary heat flow. No single coupling between phonons and the field explains all cases.","posed_since":"2005","precise":"In insulators including $\\mathrm{SrTiO_3}$, cuprate parent compounds, Kitaev candidates, garnets, quartz, MgO and intrinsic Si and Ge, fields of tens of kG produce a thermal Hall conductivity $\\kappa_{xy}$ carried by phonons, with thermal Hall angle $\\kappa_{xy}/\\kappa_{xx}$ up to $\\sim 3 \\times 10^{-3}\\text{ at }9 \\times 10^{4}\\,\\mathrm{G}$, typically peaking near the maximum of $\\kappa_{xx}$. Identify the coupling: intrinsic Berry curvature of phonon bands from spin-lattice or ionic Lorentz-type coupling, skew scattering off charged or magnetic defects, or resonant scattering by dynamical defects. An answer predicts magnitude, sign and temperature dependence across materials.","problem_ref":"cdeabbeea29a0e0a73646cc5ad97161b617805327ba35f4e49f91a7f93c949de","references":"","settled_by":"A theory predicting $\\kappa_{xy}/\\kappa_{xx}$ with sign in several unrelated insulators from measured parameters, confirmed by controlled defect doping.","status_note":"Phonon thermal Hall signals with a common scaling $\\kappa_{xy} \\sim \\kappa_{xx}^2$ were reported in many nonmagnetic crystals ($\\mathrm{SrTiO_3}$, quartz, MgO, $\\mathrm{MgAl_2O_4}$, Si, Ge; Jin et al., arXiv 2404.02863, 2024); no coupling mechanism accounts for magnitude and sign across materials.","title":"Why do phonons in many insulators show a thermal Hall 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