Mass Inversion at the Lifshitz Transition in Monolayer Graphene by Diffusive, High-Density, On-Chip Doping

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• Traditional charge transport measurements are limited by incompatibility with ultrahigh vacuum (UHV) chemical doping conditions.
• Existing field-effect methods (dielectric and ionic liquid gating) achieve insufficient carrier densities to study electronic phase transitions.

Purpose of the Study:

• To develop a method enabling charge transport measurements at ultrahigh charge carrier densities in graphene.
• To bridge the gap between UHV chemical doping and standard transport measurement setups.

Main Methods:

• An integrated flip-chip method using cesium vapor diffusion for doping monolayer graphene.
• Operando Hall measurements to monitor doping levels up to 4.7 × 10¹⁴ cm^-2.
• Transport measurements (temperature and magnetic field dependence) within a sealed, oxidation-stable assembly.

Main Results:

• Achieved ultrahigh charge carrier densities in graphene via cesium diffusion doping.
• Observed cyclotron mass inversion, indicating a Lifshitz transition at the hyperbolic M point.
• Demonstrated stability against oxidation and compatibility with standard cryogenic measurement environments.

Conclusions:

• Chemical doping of graphene is feasible in a diffusive regime at ambient pressure using alkali vapor in an inert gas environment.
• This method facilitates charge transport studies at unprecedented carrier densities in standard experimental setups.
• Enables investigation of electronic phase transitions previously inaccessible by field-effect methods.