Nonmonotonic temperature dependence of electron viscosity and crossover to high-temperature universal viscous fluid in monolayer and bilayer graphene

This paper studies the temperature dependence of viscosity and entropy density in the strong interaction regime for the electron fluid in monolayer and bilayer graphene. It demonstrates the nontrivial temperature dependence of the viscosity in the hydrodynamic regime, and calculates, via a combination of microscopic calculation of electron lifetime and the macroscopic Navier-Stokes equation, a high-temperature limit for the viscosity and entropy density. It represents a significant advancement in our understanding of the hydrodynamic electronic transport in monolayer and bilayer graphene.