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

TL;DR

This paper demonstrates how tuning the Berry phase in bilayer graphene resonators induces valley splitting and crossing, revealing new ways to manipulate valley degrees of freedom for valleytronics applications.

Contribution

It experimentally shows Berry phase-induced valley phenomena in movable bilayer graphene p-n junction resonators, a novel approach for valley control.

Findings

Giant valley splitting observed due to Berry phase tuning.

Unusual valley crossing of bound states detected.

Berry phase manipulation achieved via magnetic field in graphene resonators.

Abstract

Since its discovery, Berry phase has been demonstrated to play an important role in many quantum systems. In gapped Bernal bilayer graphene, the Berry phase can be continuously tuned from zero to 2pi, which offers a unique opportunity to explore the tunable Berry phase on the physical phenomena. Here, we report experimental observation of Berry phases-induced valley splitting and crossing in moveable bilayer graphene p-n junction resonators. In our experiment, the bilayer graphene resonators are generated by combining the electric field of scanning tunneling microscope tip with the gap of bilayer graphene. A perpendicular magnetic field changes the Berry phase of the confined bound states in the resonators from zero to 2pi continuously and leads to the Berry phase difference for the two inequivalent valleys in the bilayer graphene. As a consequence, we observe giant valley splitting and unusual valley crossing of the lowest bound states. Our results indicate that the bilayer graphene resonators can be used to manipulate the valley degree of freedom in valleytronics.