Fluidity Onset in Graphene

TL;DR

This paper reports the first direct observation of the transition to viscous electron fluid behavior in graphene, revealing a regime change from quasiballistic to hydrodynamic flow characterized by a sharp negative resistance peak.

Contribution

It demonstrates the emergence of viscous fluid behavior in an interacting electron system in graphene and characterizes the transition between quasiballistic and hydrodynamic regimes.

Findings

Negative resistance peaks at the transition point.

Viscous flow signatures appear only at high temperatures.

Resistance decreases in the hydrodynamic regime.

Abstract

Viscous electron fluids have emerged recently as a new paradigm of strongly-correlated electron transport in solids. Here we report on a direct observation of the transition to this long-sought-for state of matter in a high-mobility electron system in graphene. Unexpectedly, the electron flow is found to be interaction-dominated but non-hydrodynamic (quasiballistic) in a wide temperature range, showing signatures of viscous flows only at relatively high temperatures. The transition between the two regimes is characterized by a sharp maximum of negative resistance, probed in proximity to the current injector. The resistance decreases as the system goes deeper into the hydrodynamic regime. In a perfect darkness-before-daybreak manner, the interaction-dominated negative response is strongest at the transition to the quasiballistic regime. Our work provides the first demonstration of how the viscous fluid behavior emerges in an interacting electron system.