Berry phase is an example of anholonomy, where the phase of a quantum state may not return to its original value after its parameters cycle around a closed path; instead the quantum systems wavefunction may acquire a real measurable phase difference, referred to as a Berry phase. Berrys phase is intimately connected with the geometry of the quantum system, and measurable geometric phase effects can be seen in systems with topological singularities. Here we show that the Berry phase associated with the topological singular Dirac point in graphene gives rise to a sudden and giant increase in energy of angular momentum states in circular graphene p-n junction resonators when a critical magnetic field is reached. We demonstrate that a Berry phase can be switched on and off with small field changes on the order of 5 mT, producing modulations of quantum state energies which will prove useful in future optoelectronic graphene device applications.
Citation: Science Magazine
Pub Type: Journals
Berry phase, graphene, scanning tunneling microscopy, scanning tunneling spectroscopy, graphene resonators, graphene pn junctions