“…Another consequence of a Hall viscosity is phonon Faraday rotation, which describes the rotation of the linear polarization vector of transverse acoustic phonons due to splitting in the circularly-polarized velocities [26,72,73]. Recently, the thermal Hall effect has emerged as a powerful probe of neutral excitations such as spinons, prompting extensive experimental and theoretical studies in a variety of correlated quantum materials, including the cuprate superconductors [31,34,[74][75][76][77][78][79] and Kitaev materials like α-RuCl 3 [70,[80][81][82][83][84][85][86][87][88][89]. Here, we observe that a phonon Hall viscosity, in general, implies a nonzero phonon thermal Hall conductivity by imparting a Berry curvature to the phonon energy bands.…”