Superballistic flow of viscous electron fluid through graphene constrictions

TL;DR

This study demonstrates that viscous electron flow in graphene constrictions leads to increased conductance with temperature, surpassing free-electron limits, due to collective electron behavior that shields momentum loss.

Contribution

We experimentally show viscous electron flow effects in graphene constrictions, revealing conductance enhancement and collective electron behavior at elevated temperatures.

Findings

Conductance increases with temperature below 150 K.

Measured conductance exceeds free-electron maximum.

Viscous effects enable high-mobility transport at higher temperatures.

Abstract

Electron-electron (e-e) collisions can impact transport in a variety of surprising and sometimes counterintuitive ways. Despite strong interest, experiments on the subject proved challenging because of the simultaneous presence of different scattering mechanisms that suppress or obscure consequences of e-e scattering. Only recently, sufficiently clean electron systems with transport dominated by e-e collisions have become available, showing behavior characteristic of highly viscous fluids. Here we study electron transport through graphene constrictions and show that their conductance below 150 K increases with increasing temperature, in stark contrast to the metallic character of doped graphene. Notably, the measured conductance exceeds the maximum conductance possible for free electrons. This anomalous behavior is attributed to collective movement of interacting electrons, which 'shields' individual carriers from momentum loss at sample boundaries. The measurements allow us to identify the conductance contribution arising due to electron viscosity and determine its temperature dependence. Besides fundamental interest, our work shows that viscous effects can facilitate high-mobility transport at elevated temperatures, a potentially useful behavior for designing graphene-based devices.