Probing Graphene Hydrodynamics with a Carbon Nanotube via Coulomb Drag

In the hydrodynamic regime, where the electron-electron scattering length is smaller than the elastic scattering length, the collective behavior of the electrons in graphene is predicted to resemble a viscous fluid. When two mesoscopic conductors are isolated but closely spaced, a current driven in one layer induces a current in the proximate conducting layer via the Coulomb interaction between electrons in different layers. This Coulomb drag effect has been shown to occur between carbon nanotubes and graphene separated by a few-layer hexagonal boron nitride crystal. We employ an individually isolated carbon nanotube as a controllable 1D perturbation to create the shearing drag forces in the graphene that result in the viscous behaviors characteristic of the hydrodynamic regime. By examining the spatial dependence of the drag signal, we can deduce the pattern of the hydrodynamic flow in graphene at different doping levels. Our preliminary results at high carrier density (in the Fermi liquid regime) indicate sign changes of the drag response as distance from the carbon nanotube-induced current increases.