Event
MSE Seminar - Dr. Joseph A. Stroscio, National Institute of Standards and Technology
Friday, April 24, 2009
1:00 p.m.
Room 2108, Chemical and Nuclear Engineering Bldg.
Annette Mateus
301 405 5207
amateus@umd.edu
"Observing the Quantization of Zero Mass Carriers in Graphene"
Application of a magnetic field to conductors causes the charge carriers to circulate in cyclotron orbits with quantized energies called Landau levels (LLs). The Landau levels are equally spaced in normal metals and two dimensional electron gases. In graphene however, the charge carrier velocity is independent of their energy (like massless photons). Consequently, the Landau level energies are not equally spaced and include a new characteristic zero energy state (the n=0 Landau level). Using scanning tunneling spectroscopy of graphene grown on silicon carbide, we directly observe non-equally spaced energy level spectrum of Landau levels, including the hallmark zero-energy state of graphene. We measure the local variation in the electrostatic potential of graphene by spatially mapping the n=0 Landau level. As the magnetic field is varied at fixed tunneling energy, new oscillations are detected in the tunneling conductance, which are shown to be a method to measure low energy electronic band structure. These tunneling magneto-conductance oscillations are used to determine the linear energy-momentum dispersion of graphene through the Dirac point with extremely high energy and momentum resolution.
