Bilayer graphene as a model hydrodynamic conductor

This talk will describe our work establishing bilayer graphene as a model hydrodynamic semiconductor, in which carrier-carrier collisions play a dominant role in determining the conductivity over a wide range of temperature and carrier density. We measure conductivity of ultraclean bilayer graphene encapsulated within hBN, with dual gates providing independent control over carrier density and bandgap. At charge neutrality, the conductivity is temperature-independent over a wide range to above room temperature, with a magnitude predicted for electron hole scattering. This behavior cannot be accounted for by dissipative scattering from impurities or phonons. In the gapped regime, the charge-neutral conductivity shows scaling behavior predicted by electron-hole scattering. Away from charge neutrality, a two-fluid model is required to accurately reflect the interaction between electron between electron-hole and dissipative scattering mechanisms. In bilayer graphene, a simple limit this model provides quantitative agreement with experiments at all densities, temperatures, and band gaps, using a single set of four parameters. The model allows mapping of the phase space for hydrodynamic conductivity for different disorder levels, and is straightforward to extend to new materials.