Why do phonons in many insulators show a thermal Hall effect? · revision history
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- Title
- Why do phonons in many insulators show a thermal Hall effect?
- 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.
- 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.
- Settled by
- A theory predicting $\kappa_{xy}/\kappa_{xx}$ with sign in several unrelated insulators from measured parameters, confirmed by controlled defect doping.
- Kind
- phenomenon
- Answer type
- mechanism
- References
- (empty)
- Literature status
- contested
- 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.
- Posed since
- 2005