The phonon Hall viscosity of ionic crystals

TL;DR

This paper investigates the phonon Hall viscosity in ionic crystals, showing it arises from Lorentz forces on ions, and provides calculations and comparisons with other mechanisms.

Contribution

It introduces a new mechanism for phonon Hall viscosity in ionic crystals caused by Lorentz forces, with quantitative estimates and comparisons.

Findings

Lorentz forces induce a measurable phonon Hall viscosity

Calculated values suggest significance relative to other mechanisms

Comparison indicates potential dominance in certain conditions

Abstract

When time-reversal symmetry is broken, the low-energy description of acoustic lattice dynamics allows for a dissipationless component of the viscosity tensor, the phonon Hall viscosity, which captures how phonon chirality grows with the wavevector. In this work, we show that, in ionic crystals, a phonon Hall viscosity contribution is produced by the Lorentz forces on moving ions. We calculate typical values of the Lorentz force contribution to the Hall viscosity using a simple square lattice toy model, and we compare it with literature estimates of the strengths of other Hall-viscosity mechanisms.