Evidence for Local Spots of Viscous Electron Flow in Graphene at Moderate Mobility

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• Dominant electron-electron scattering facilitates viscous electron flow, leading to hydrodynamic current patterns like Poiseuille profiles.
• Recent experiments in graphene have confirmed the viscous electron flow regime through transport measurements and Poiseuille profile mapping.

Purpose of the Study:

• To investigate current-induced surface potential maps in moderate-mobility graphene field-effect transistors at room temperature.
• To identify and characterize regions exhibiting hydrodynamic electron flow.
• To understand the role of electron-electron scattering in these phenomena.

Main Methods:

• Utilizing scanning probe microscopy to map current-induced surface potentials in graphene field-effect transistors.
• Estimating local scattering lengths by analyzing the gate dependence of local in-plane electric fields.
• Modifying electron-disorder scattering length via ion bombardment to observe its effect on electric fields.

Main Results:

• Discovery of micrometer-sized areas near charge neutrality exhibiting electric fields that oppose the applied external field.
• Confirmation that electron-electron scattering dominates in these areas, consistent with viscous flow.
• Suppression of the observed inverted fields upon reducing the electron-disorder scattering length.

Conclusions:

• Viscous electron flow is prevalent in graphene devices, extending to those with moderate mobility.
• The findings provide evidence for ubiquitous hydrodynamic electron behavior in graphene.
• Electron-electron scattering plays a crucial role in enabling viscous electron flow in graphene.