Hall viscosity in altermagnets

Altermagnetic states, which are invariant under a combination of time-reversal and real-space rotation, have attracted considerable interest from the condensed matter physics community. One of the main signatures of this type of compensated collinear magnetic order is the nodal spin-splitting pattern of their band dispersion which, however, is challenging to be measured experimentally. In this talk, we will show that, under certain conditions, the onset of altermagnetic order results in Hall viscosity, corresponding to the dissipationless generation of strain by a time-varying stress. Specifically, we classify the different types of Hall viscosity coefficients that emerge for distinct types of altermagnetic order and compute their manifestation through the acoustic Faraday effect for selected candidate materials.