Visualizing Poiseuille flow of hydrodynamic electrons

Area of Science:

• Condensed Matter Physics
• Quantum Electronics
• Materials Science

Background:

• Hydrodynamics typically describes fluid flow, but its principles are increasingly observed in electron systems under specific conditions.
• Previous experiments hinted at electron hydrodynamics, yet direct visualization of its characteristic spatial structure, the Poiseuille flow, remained a challenge.

Purpose of the Study:

• To directly image the Poiseuille flow profile of electronic fluid in graphene.
• To visualize the transition between ballistic and hydrodynamic electron flow regimes.
• To experimentally confirm Poiseuille flow in a solid-state system.

Main Methods:

• Utilized a scanning carbon nanotube single-electron transistor for high-resolution imaging.
• Measured the Hall voltage across high-mobility graphene channels to probe electronic flow.
• Analyzed the spatial profile of the Hall field to distinguish flow regimes.

Main Results:

• Directly imaged parabolic Hall field profiles, indicative of Poiseuille flow, at elevated temperatures.
• Observed a transition from flat, ballistic field profiles at low temperatures to these parabolic profiles.
• Qualitatively reproduced the observed flow profiles using Boltzmann calculations, enabling a phase diagram of electron flow regimes.

Conclusions:

• Provided direct experimental confirmation of Poiseuille flow in solid-state electronic systems.
• Demonstrated that the Hall field profile is a key indicator for distinguishing ballistic from hydrodynamic electron flow.
• Opened new possibilities for exploring the physics of interacting electrons in real space.