{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"62a6f7ea0d4397748b13aa35603a45da5d75e5662d2f63fa15684fbfee015b62","created":"2026-10-03T07:18:01Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"0716682129d7ca9d052bfee470185f405a70f87ae7ceb8183ed84dd51310ac4a","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":"1","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 SrTiO3, 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 $\\sim 3e-3\\text{ at }9e4\\,\\mathrm{G}$, 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":null,"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 (SrTiO3, quartz, MgO, MgAl2O4, 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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