Movable Valley Switch Driven by Berry Phase in Bilayer-Graphene Resonators

Area of Science:

• Quantum physics
• Condensed matter physics
• Materials science

Background:

• The Berry phase is a fundamental geometric phase in quantum mechanics, crucial for understanding various quantum systems.
• Gapped Bernal bilayer graphene exhibits a continuously tunable Berry phase (0 to 2π), offering a unique platform for exploring its physical implications.

Purpose of the Study:

• To experimentally observe and investigate Berry-phase-induced phenomena in bilayer graphene.
• To demonstrate the potential of bilayer graphene p-n junction resonators for controlling quantum properties.

Main Methods:

• Fabrication of movable bilayer graphene p-n junction resonators using a scanning tunneling microscope tip and applied electric field.
• Application of a perpendicular magnetic field to tune the Berry phase of confined bound states.
• Observation of valley splitting and crossing phenomena in the lowest bound states.

Main Results:

• Continuous tuning of the Berry phase from 0 to 2π was achieved by varying the magnetic field.
• Giant valley splitting and unusual valley crossing of the lowest bound states were experimentally observed.
• The Berry phase difference between the two inequivalent valleys in bilayer graphene was induced.

Conclusions:

• Bilayer graphene resonators provide a novel platform for manipulating the Berry phase and its associated quantum effects.
• The observed phenomena highlight the potential of these resonators for applications in valleytronics, controlling the valley degree of freedom.