November 8, 2006
InterSchool Lab, 7th floor, Schapiro/CEPSR
Hosted by: Phillip Kim - CISE
Speaker: Eli Rotenberg, Lawrence Berkeley National Laboratory
Graphene, a single layer of carbon atoms arranged in a simple honeycomb lattice, is the building block of graphite, fullerenes, and carbon nanotubes and has fascinating electronic properties. Of fundamental interest is the effectively massless, relativistic character of its charge carriers. This arises as a result of its unique electronic structure, characterized by conical valence and conduction bands that meet at a single point in momentum space (at the Dirac crossing energy). Of practical interest is the fact that its carrier motion is ballistic at room temperature, making graphene potentially useful for ultrasmall, ultrafast computing devices. I will describe the synthesis of graphene thin films (from one to four layers) grown on insulating silicon carbide wafers and report the evolution of their electronic band structure using angle-resolved photoemission spectroscopy (ARPES). For monolayer graphene, we can determine the electronic spectral function, which encodes the many-body interactions amongst the quasiparticles in the system-namely the charge and vibrational excitations. Our measurements show that the bands around the Dirac crossing point are heavily renormalized by electron-electron, electron-plasmon, and electron-phonon coupling, showing that these interactions must be considered on an equal footing in attempts to understand the quasiparticle dynamics in graphene and related systems. For bilayer graphene, I will describe the electronic band structure as a function of doping. By selectively adjusting the carrier concentration in each layer, changes in the layer-dependent Coulomb potential lead to a control of the gap between valence and conduction bands. This control over the band structure suggests potential application of bilayer graphene to switching functions in atomic-scale electronic devices.
 Bostwick, A., Ohta, T., Seyller, T., Horn, K. & Rotenberg, E. Quasiparticle Dynamics in Graphene. Nature Physics, in press.
 Ohta, T., Bostwick, A., Seyller, T., Horn, K. & Rotenberg, E. Controlling the Electronic Structure of Bilayer Graphene. Science 313, 951-954 (2006).