Why do phonons in many insulators show a thermal Hall effect? · revision history

Revision 2

Accepted · core change · record

Changes against revision 1:

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 · changed · core
Revision 1: 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.
Revision 2: 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.
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 · changed
Revision 1: 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.
Revision 2: 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.
Posed since
2005

Decisions