Coulomb drag of viscous electron fluids: drag viscosity and negative drag conductivity

TL;DR

This paper investigates how Coulomb drag in viscous electron fluids introduces new viscosity effects, including drag viscosities, which can be tuned by magnetic fields and densities, leading to phenomena like negative drag conductivity.

Contribution

It introduces drag and drag-Hall viscosities as new hydrodynamic terms caused by interlayer Coulomb interactions, expanding the understanding of electron fluid dynamics.

Findings

Drag viscosities are tunable via magnetic field and electron densities.

Negative drag conductivity occurs at specific density ratios.

Coulomb interactions modify the stress tensor in hydrodynamic equations.

Abstract

We show that Coulomb drag in hydrodynamic bilayer systems leads to additional viscosity terms in the hydrodynamic equations, i.e., the drag and drag-Hall viscosities, besides the well-known kinematic and Hall viscosities. These new viscosity terms arise from a change of the stress tensor due to the interlayer Coulomb interactions. All four viscosity terms are tunable by varying the applied magnetic field and the electron densities in the two layers. At certain ratios between the electron densities in the two layers, the drag viscosity dramatically changes the longitudinal transport resulting in a negative drag conductivity.