Graphene - a nearly perfect fluid

TL;DR

This paper calculates the shear viscosity to entropy density ratio in clean graphene, revealing it is exceptionally low and close to the conjectured quantum lower bound, with implications for fluid dynamics.

Contribution

It provides the first quantum kinetic theory calculation of ta/s in graphene, highlighting its near-perfect fluid behavior due to quantum criticality.

Findings

ta/s in graphene is smaller than in many correlated liquids

The ratio approaches the lower bound conjectured for quantum fluids

Potential for pre-turbulent current flow in graphene

Abstract

Hydrodynamics and collision dominated transport are crucial to understand the slow dynamics of many correlated quantum liquids. The ratio \eta/s of the shear viscosity \eta to the entropy density s is uniquely suited to determine how strongly the excitations in a quantum fluid interact. We determine \eta/s in clean undoped graphene using a quantum kinetic theory. As a result of the quantum criticality of this system the ratio is smaller than in many other correlated quantum liquids and, interestingly, comes close to a lower bound conjectured in the context of the quark gluon plasma. We discuss possible consequences of the low viscosity, including pre-turbulent current flow.