Condensed Matter Journal Club: "Anomalous Hall viscosity in altermagnets: microscopic origins and acoustic probes"

Abstract: In this talk, I will develop a theoretical framework for anomalous Hall viscosity in altermagnets and propose acoustic protocols for its detection. I will show that its symmetry-allowed tensor structure distinguishes altermagnets from ferromagnets and conventional antiferromagnets, while microscopic calculations reveal a strong sensitivity to gapped Dirac points and Lifshitz transitions. I will then discuss a polarization-resolved acoustic Faraday experiment and identify complementary measurement protocols: one that directly isolates Hall-viscosity-induced mode mixing, and another that exploits elastic anisotropy to enhance the Hall-viscosity contribution through interference with the elastic background, thereby facilitating its experimental detection. These results establish Hall viscosity as both a probe of altermagnetic symmetry and electronic topology and a measurable quantity in GHz ultrasound experiments.