Exploring the charge dynamics in graphite nanoplatelets by THz and infrared spectroscopy

We present the results of THz, infrared and magneto-optical measurements performed on graphite nanoplatelet films as a function of temperature (4.2-300 K) and magnetic field (0-17.5 T). An effective medium analysis of the low-energy spectral response indicates that the nanoplatelet material is well described by a Drude function plus two infrared absorption bands. Interestingly, the Drude plasma frequency (∼1675 cm^-1) decreases slowly with temperature, whereas the carrier scattering rate (∼175 cm^-1) is temperature independent. Furthermore, measurements in an applied magnetic field at 4.2K show that a large portion of the Drude spectral weight is transferred to finite frequency features corresponding to various Landau-level transitions. Some of these transition energies scale as p B, as expected for Dirac-like quasi-particles in graphene and observed in other graphene-like materials. Thus, our results are consistent with recent theoretical calculations indicating that the spectrum of multilayer graphene can be decomposed into subsystems effectively identical to monolayer or bilayer graphene.