Doping-driven topological polaritons in graphene/α-MoO₃ heterostructures

Area of Science:

• Photonics and Materials Science
• Condensed Matter Physics

Background:

• Charge carrier density is a key parameter for tuning material properties and inducing phase transitions.
• Topological transitions in optical responses of photonic systems can be achieved by controlling material properties.

Purpose of the Study:

• To investigate topological transitions in hybrid polaritons within a 2D heterostructure.
• To explore the influence of graphene doping on polariton dispersion and topology.
• To demonstrate tunable diffractionless polariton propagation and subwavelength focusing.

Main Methods:

• Fabrication of a 2D heterostructure comprising graphene and α-phase molybdenum trioxide.
• Chemical modification of graphene's doping level to alter charge carrier density.
• Analysis of polariton isofrequency dispersion contours and their topological evolution.
• Utilizing a silica substrate as an in-plane lens for polariton focusing.

Main Results:

• Observed a topological transition in polariton isofrequency surfaces from open to closed shapes due to doping-dependent hybridization.
• Demonstrated tunable diffractionless polariton propagation by modifying the substrate and achieving flat dispersion contours.
• Achieved subwavelength focusing of polaritons to 4.8% of the free-space wavelength.

Conclusions:

• Graphene doping provides precise control over polariton topology and optical properties.
• The system supports tunable diffractionless propagation and local control of optical contour topology.
• Findings pave the way for on-chip applications in nanoimaging, sensing, and nanoscale energy transfer manipulation.