Charged defects and phonon Hall effects in ionic crystals
Benedetta Flebus, A. H. MacDonald
Abstract
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 ${\ensuremath{\kappa}}_{H}$ to the phonon longitudinal conductivity ${\ensuremath{\kappa}}_{L}$ in oxide dielectrics that are larger than ${10}^{\ensuremath{-}3}$ when phonon mean-free paths exceed phonon wavelengths. At the same time ${\ensuremath{\kappa}}_{H}/{\ensuremath{\kappa}}_{L}$ 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.