How close can one approach the Dirac point in graphene experimentally?

Area of Science:

• Condensed matter physics
• Quantum physics
• Materials science

Background:

• Graphene is a key material for studying relativistic quantum physics.
• Understanding its electronic properties is crucial for theoretical and experimental research.

Purpose of the Study:

• To experimentally investigate electron transport in suspended graphene devices.
• To determine the intrinsic electronic properties of graphene at various temperatures.
• To explore the limits of charge inhomogeneity and potential bandgaps.

Main Methods:

• Fabrication of suspended graphene devices.
• Measurement of electron transport properties.
• Analysis of Landau quantization and charge inhomogeneity.
• Temperature-dependent measurements from 1 K to above liquid helium temperatures.

Main Results:

• Achieved carrier mobilities of several 10^6 cm^2 V^-1 s^-1.
• Observed Landau quantization onset below 5 mT.
• Measured low charge inhomogeneity (≈10^8 cm^-2).
• Demonstrated intrinsic electronic properties above liquid helium temperatures.
• Approached the Dirac point within 1 meV.

Conclusions:

• Graphene's electronic properties are intrinsic and governed by thermal excitations above liquid helium temperatures.
• The study establishes an upper limit on a possible bandgap, showing no insulating state down to 1 K.
• Experimental findings provide insights into graphene's behavior as a model system for relativistic quantum physics.