Out-of-bounds hydrodynamics in anisotropic Dirac fluids

Understand

We study the hydrodynamic behavior in two-dimensional, interacting electronic systems with merging Dirac points at charge neutrality.

• The dispersion along one crystallographic direction is Dirac-like, while it is Newtonian-like in the orthogonal direction.
• As a result, the electrical conductivity is metallic in one and insulating in the other direction.
• One element of the shear viscosity tensor violates the famous lower bound for the shear viscosity to entropy density ratio,an effect that can be probed via anisotropic thermal Hagen- Poiseuille flow.