Evidence for Interlayer Electronic Coupling in Multilayer Epitaxial   Graphene from Polarization Dependent Coherently Controlled Photocurrent   Generation
  Most experimental studies to date of multilayer epitaxial graphene on C-face SiC have indicated that the electronic states of different layers are decoupled as a consequence of rotational stacking. We have measured the third order nonlinear tensor in epitaxial graphene as a novel approach to probe interlayer electronic coupling, by studying THz emission from coherently controlled photocurrents as a function of the optical pump and THz beam polarizations. We find that the polarization dependence of the coherently controlled THz emission expected from perfectly uncoupled layers, i.e. a single graphene sheet, is not observed. We hypothesize that the observed angular dependence arises from weak coupling between the layers; a model calculation of the angular dependence treating the multilayer structure as a stack of independent bilayers with variable interlayer coupling qualitatively reproduces the polarization dependence, providing evidence for coupling. 
Dong Sun, Julien Rioux, J. E. Sipe, Yang Zou, Momchil Mihnev, Claire   Berger, Walt A. de Heer, Phillip N. First, and Theodo...
cond-mat.mes-hall cond-mat.mtrl-sci