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Past Events
Whispering Galleries in Circular Graphene Resonators and their Evolutions under Magnetic Field
| Speaker: | Dr. Yue Zhao |
| Affiliation: | Department of Physics, Southern University of Science and Technology |
| Date: | November 3, 2017 (Friday) |
| Time: | 4:30 p.m. |
| Venue: | Room 522, 5/F, Chong Yuet Ming Physics Building, HKU |
Abstract
Graphene provides an ideal platform for electron optics due to its light-like dispersion. Because of Klein tunneling, highly transparent pn junctions can be created by electron static gating. Electron reflections and transmissions at the boundaries can be manipulated by gate potential, enabling the quantum interference of electron waves. In analogy with optical wave propagations, Fabry-Perot interferences and Veselago lensing of carriers in graphene can be achieved in linear pn junctions. In circular geometries, the localized Dirac fermions can induce whispering gallery modes (WGM)[1][2], similar to acoustic whispering galleries. In this talk, I will discuss the whispering gallery modes in our circular graphene resonators created by a local STM probe, as well as how the WGM states evolve under varying magnetic fields. Under a small critical magnetic field, a giant and discontinuous change in the energy of time reversed angular momentum states emerges, which is attributed to the switching of the berry phase in the circular graphene resonators[3][4]. I will also show observations of modified Landau levels created by the STM probe potential when the magnetic field is much larger than the critical value.
[1] Zhao et al. Science 348, 6235, 672-675 (2015)
[2] Lee et al. Nature Physics 12, 1032 (2016)
[3] J. F. Rodriguez-Nieva and L. S. Levitov, Phys. Rev. B 94, 235406 (2016)
[4] Ghahari et al. Science 356, 6340, 845-849 (2017)
Anyone interested is welcome to attend.