Out-of-equilibrium criticalities in graphene superlattices

Area of Science:

• Condensed Matter Physics
• Materials Science
• Graphene Superlattices

Background:

• In equilibrium, metallic conduction relies on electrons near the Fermi energy.
• Deeper filled bands typically contribute minimally to electrical current.
• Understanding non-equilibrium electronic states is crucial for novel device functionalities.

Purpose of the Study:

• To investigate carrier distribution and conduction mechanisms in graphene superlattices under extreme non-equilibrium conditions.
• To identify and characterize a novel conductive regime beyond traditional thermodynamic equilibrium.
• To explore the implications of filled bands contributing significantly to current.

Main Methods:

• Fabrication and characterization of graphene superlattice devices.
• Measurement of current-voltage characteristics under varying conditions.
• Analysis of differential resistance, Hall effect, and related phenomena to probe electronic states.

Main Results:

• Observation of a distinct non-equilibrium state where filled bands actively participate in conduction.
• Emergence of critical-current behavior as electron velocity approaches Fermi velocity.
• Identification of key signatures including superconductor-like I-V curves, resistance peaks, Hall effect sign reversal, and Schwinger-like plasma production.

Conclusions:

• Graphene superlattices can be driven into a non-equilibrium state with significant conduction from filled bands.
• This state exhibits critical-current properties and unique electronic signatures.
• The observed phenomena are expected to be a general characteristic of graphene-based superlattices.