4 p.m. - 5 p.m. Location: SLC 1.102
Dr. Zhigang Jiang (Georgia Tech)
Probing energy, symmetry and dispersion of low-lying excitations (e.g., electrons, holes, plasmons, phonons) in solids and studying many-body interactions among them and with light are focal points of our research. Here we first report on the observation of plasmon-type collective excitations in quasi-neutral graphene nanoribbons exposed to a perpendicular magnetic field. Most saliently, we reveal a peculiar scaling behavior which allows us to identify this mode with the upper-hybrid mode (UHM) between the plasmon resonance and the lowest Landau level (LLL) transition in graphene. This scaling is different from that of the UHM in conventional two-dimensional electron gases with parabolic bands or in highly doped graphene as well as from that of magnetoexcitons. Second, we show that similar hybrid modes between the K-point optical phonons in graphite and the LLL transition may form when the inter-LL transition energy is tuned to cross the optical phonon energy by varying the magnetic field. In this case, a marked avoided-level-crossing splitting of the cyclotron resonance is observed, and the strength of electron-phonon interactions is obtained from the amplitude of the splitting.