Hydrodynamics in graphene: Linear-response transport

We develop a hydrodynamic description of transport properties in graphene-based systems which we derive from the quantum kinetic equation. In the interaction-dominated regime, the collinear scattering singularity in the collision integral leads to fast unidirectional thermalization and allows us to describe the system in terms of three macroscopic currents carrying electric charge, energy, and quasiparticle imbalance. Within this "three-mode" approximation we evaluate transport coeffcients in monolayer graphene as well as in double-layer graphene-based structures. The resulting classical magnetoresistance is strongly sensitive to the interplay between the sample geometry and leading relaxation processes. In small, mesoscopic samples the macroscopic currents are inhomogeneous which leads to linear magnetoresistance in classically strong fields. Applying our theory to double-layer graphene-based systems, we provide microscopic foundation for phenomenological description of giant magnetodrag at charge neutrality and find magnetodrag and Hall drag in doped graphene.