National Synchrotron Light Source

"Magneto-Spectroscopy Studies of Graphite Nanoplatelet Films"

H. L. Liu^a,b

In collaboration with G. L. Carr^b, K. A. Worsley^c, M. E. Itkis^c, E. Bekyarova^c, R. C. Haddon^c, A. N. Caruso^d, L.-C. Tung^e, and Y.-J. Wang^e

^aDepartment of Physics, National Taiwan Normal University, Taiwan
^bNational Synchrotron Light Source, Brookhaven National Laboratory, USA
^cDepartment of Chemistry, University of California-Riverside, USA
^dDepartment of Physics, University of Missouri-Kansas City, USA
^eNational High Magnetic Field Laboratory, USA

The very peculiar transport and electrodynamic properties of the atomically thin graphene films have been intensively studied in the past few years. While the ideal case of a single, isolated graphene sheet having macroscopic dimensions is difficult to realize, systems comprised of multiple graphene sheets can still show some of these peculiar properties. We have undertaken an infrared and magnetic-field study of moderately thick graphene films consisting of ~1.7 nm thick nanoplatelet structures. Our far-infrared results yield an electronic scattering rate of 780 cm^-1 (1.5 x 10¹⁴ rad/s) and plasma frequency of 3650 cm^-1, the latter decreasing slowly with temperature. Magneto-spectroscopy measurements at 4.2 K and in magnetic fields up to B = 17.5 T show several sets of Landau level transitions (cyclotron resonance). The frequencies for some of these transitions scale as B^1/2, indicating a significant contribution from nearly massless Dirac Fermions (quasiparticles obeying a linear dispersion relation). This opens the possibility for observing a strong non-linear optical response in the THz spectral range, as proposed by S. A. Mikhailov (EPL, 79 27002 2007).

Research at the NSLS is supported by the Department of Energy under contract DE-AC02-98CH10886.