Dr. Erik Henriksen
Department of Physics
CALTECH

Cyclotron Resonance in Graphene

Abstract:

Graphene, a single-atom thick allotrope of carbon, is the newest and thinnest member of the family of two-dimensional systems. Interest in graphene has soared since the discovery of a new manifestation of the quantum Hall [1,2]. Recently we have explored the energy spectrum of single layer graphene at high magnetic fields, by measuring the cyclotron resonance (CR) via absorption of infrared light. We find the Landau level (LL) energies exhibit a highly unusual square root dependence on the LL index, n, as well as a square root dependence on the applied magnetic field. These results have been anticipated since 1956 [3], and are quite distinct from familiar semiconductor systems 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 see evidence of contributions to the CR energy from electron-electron interactions, which are suppressed in CR of traditional semiconductors as desribed by Kohn's theorem [4]. The lack of a similar restriction in graphene suggests CR measurements can open a new window into many-particle physics in this exciting material.

1 K.S. Novoselov et al, Nature 438, 197 (2005).
2 Y. Zhang et al, Nature 438, 201 (2005).
3 J. McClure, PR 104, 666 (1956).
4 W. Kohn, PR 123, 1242 (1961).