It has been known for decades that a magnetic field can deflect phonons as they flow in response to a thermal gradient, producing a thermal Hall effect. Several recent experiments have revealed ratios of the phonon Hall conductivity ${\kappa }_H$ to the phonon longitudinal conductivity ${\kappa }_L$ in oxide dielectrics that are larger than ${10}^{-3}$ when phonon mean-free paths exceed phonon wavelengths. At the same time ${\kappa }_H/{\kappa }_L$ is not strongly temperature dependent. We argue that these two properties together imply a mechanism related to phonon scattering from defects that break time-reversal symmetry, and we show that Lorentz forces acting on charged defects can produce substantial skew-scattering amplitudes and related thermal Hall effects.

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• Lattice dynamics
• Lattice thermal conductivity
• Phonons
• Thermal Hall effect
• Thermomagnetic effects
• Ionic solids