Distinguishing viscous, ballistic, and diffusive current flows in anisotropic metals

TL;DR

This paper demonstrates that local imaging can differentiate between ballistic, viscous, and ohmic current flows in anisotropic metals, especially in graphene heterostructures, aiding direct measurement of scattering lengths.

Contribution

It introduces a method to distinguish flow regimes in anisotropic Fermi liquids via imaging, and proposes graphene heterostructures as a platform for observing these effects.

Findings

Imaging can distinguish flow regimes in anisotropic metals.

Graphene heterostructures can exhibit a ballistic-to-viscous crossover.

Potential for direct measurement of scattering lengths.

Abstract

We show that in anisotropic Fermi liquids where momentum-conserving scattering is much faster than momentum-relaxing scattering processes, local imaging of the electric current flow patterns can cleanly distinguish between ballistic, viscous and ohmic flow patterns simultaneously (using a single image). We propose using multi-layer graphene-based heterostructures, including ABA trilayer graphene, as a natural experimental platform where an anisotropic ballistic-to-viscous crossover may be visible in near-term experiments. Such experiments could lead to more direct measurements of momentum-conserving scattering lengths in electronic Fermi liquids.