Superconductivity and quantized anomalous Hall effect in rhombohedral graphene

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Physics

Background:

• Superconducting correlations in chiral edge states are predicted to yield topologically protected zero energy modes.
• Existing experimental methods often suffer from interfacial disorder, hindering the formation of isolated topological modes.
• Low-density flat band materials offer a promising alternative for tuning between superconducting and quantum anomalous Hall states via electric fields.

Purpose of the Study:

• To achieve simultaneous quantized transport and superconductivity in a low-disorder system.
• To explore the potential of engineered graphene heterostructures for topological quantum phenomena.
• To investigate the tunability and reconfigurability of topological edge states.

Main Methods:

• Fabrication of rhombohedral tetralayer graphene aligned to hexagonal boron nitride.
• Utilizing electric field effect for tuning material states.
• Employing thermodynamic compressibility measurements.
• Integrating transition metal dichalcogenide layers.

Main Results:

• Observation of a quantum anomalous Hall state at ν = -1 and a superconducting state at ν ≈ -3.5 in rhombohedral tetralayer graphene at zero magnetic field.
• Demonstration of non-volatile switching of quantum anomalous Hall state chirality via gate voltage.
• Identification of a fractional Chern insulator at ν = 2/3 with fractional charge.
• Nucleation of a new superconducting pocket by integrating transition metal dichalcogenide layers without disrupting the quantum anomalous Hall state topology.

Conclusions:

• The engineered graphene heterostructure successfully hosts coexisting quantum anomalous Hall and superconducting states at zero magnetic field, overcoming previous disorder limitations.
• The system allows for tunable and reconfigurable topological edge modes, opening possibilities for novel quantum device architectures.
• The findings enable proximity coupling between superconductivity and fractionally charged edge modes, advancing the study of topological quantum matter.