``Intrinsic'' terahertz plasmons and magnetoplasmons in single layer graphene on SiC

Plasmons in graphene have lately attracted much attention, to great extent, due to promises for novel technologies. Recently, plasmon absorption in graphene was attained in deliberately patterned structures [1]. We measured the magneto-optical absorption and Faraday rotation response of highly doped single layer graphene, epitaxially grown on Si-terminated SiC substrate. The zero-field spectra show a clear plasmon peak at about 2 THz. In magnetic fields, the plasmon peak splits into two branches, thus showing a characteristic magneto-plasmon behavior which was previously observed in periodic dot structures in GaAs two dimensional electron gases [2]. Hence, in large-scale epitaxial graphene on SiC, light can couple to plasmons in the absence of the intentional patterning of graphene. We suggest that optically-active plasmon absorption in this kind of two-dimensional system arises from laterally confined plasmon modes due to``intrinsic'' imperfections of graphene on Si-face of SiC, such as, grain boundaries which we clearly identify with AFM methods. \newline\noindent [1] L. Ju \emph{et al.} , Nature Nanotechnology \textbf{6}, 630 (2011). \newline\noindent [2] A. J. Allen \emph{et al.} , Phys Rev B \textbf{28}, 4875 (1983).