Out-of-bounds hydrodynamics in anisotropic Dirac fluids

TL;DR

This paper investigates the unique hydrodynamic properties of anisotropic Dirac fluids with merging Dirac points, revealing directional conductivity differences and a violation of the shear viscosity bound, with potential experimental implications.

Contribution

It introduces the concept of out-of-bounds hydrodynamics in anisotropic Dirac systems, highlighting directional transport properties and viscosity bound violation.

Findings

Electrical conductivity is metallic in one direction and insulating in the orthogonal direction.

Shear viscosity tensor element violates the lower bound for viscosity to entropy density ratio.

Anisotropic thermal Hagen-Poiseuille flow can probe these effects.

Abstract

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.