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Experimental measurement of anisotropic viscosity tensor components

Measure the nontrivial components of the fourth-rank viscosity tensor in anisotropic electron fluids that lack rotational symmetry, and quantify their role in transport.

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Background

In crystalline materials, rotational symmetry is broken and viscosity becomes a full rank-4 tensor with multiple independent components. Theory has analyzed such anisotropic viscous responses, but direct experimental measurements remain absent. Measuring these components would test predictions and refine hydrodynamic modeling in real crystals.

References

These components have been studied a number of works though have yet to be experimentally measured.

— Hydrodynamics of the electronic Fermi liquid: a pedagogical overview (2504.01249 - Hui et al., 1 Apr 2025) in Section “Symmetry-breaking and the viscosity tensor” (subsection of Beyond Isotropic Fermi Liquid Hydrodynamics)