Event

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 system’s wave function may acquire a real, measurable phase difference, known as Berry phase. Berry phase is connected with the geometry of the quantum system having intriguing physical consequences in systems with topological singularities, such as graphene.  In this talk, I will present spectroscopic measurements of the quasi-bound resonances originating from Klein scattering in circular graphene p-n junction resonators. Our results demonstrate a giant and discontinuous change in the energy of time-reversed angular-momentum states as a function of magnetic field, which manifests itself as the appearance of “new” resonances in the tunneling density of states. This behavior corresponds to the On/Off switching of a π- Berry phase when a weak critical magnetic field is reached.  Experimentally, the electronic states can be switched on and off with small magnetic field changes on the order of 5 mT, producing strong modulation of quantum state energies with possible technical applications.