MONDAY, April 6
Condensed Matter Physics Seminar, 4:00 PM - 5:00 PM, 107 Downs
"Cyclotron Resonance in Graphene," Erik Henriksen, Caltech. More info: CMP

Abstract:
Graphene, a single-atom thick allotrope of carbon, is the newest member of the family of two-dimensional systems. Interest in graphene has soared since the discovery of a new manifestation of the quantum Hall effect \cite{novoselov05, zhang05}. The low energy, {\it linear} dispersion of graphene is highly unusual, giving rise to excitations analogous to massless chiral Dirac fermions. Recently we have explored the magnetic energy spectra of single layer graphene, by measuring the cyclotron resonance (CR) via absorption of infrared light. Our results have confirmed the unusual dependence of the Landau level (LL) energies on the LL index, as well as a square root dependence on the applied magnetic field. This spectrum is quite distinct from more familiar systems with quadratic dispersions, in which an evenly spaced set of LLs shows a linear field dependence. In addition, we find significant departures from the CR expected for single layer graphene in the lowest order tight-binding model. In particular, we find evidence of contributions to the CR energy from electron-electron interactions, which are generally suppressed in traditional parabolic semiconductors due to Kohn's theorem \cite{kohn}. The lack of a similar Kohn's theorem for graphene suggests CR measurements can open a new window into many-particle physics in this exciting material.

Sponsored by Gil Refael