We demonstrate that plasmons in graphene can be manipulated using a DC current. A sourcedrain current lifts the forward/backward degeneracy of the plasmons, creating two modes with different propagation properties parallel and antiparallel to the current. We show that the propagation length of the plasmon propagating parallel to the drift current is enhanced, while the propagation length for the antiparallel plasmon is suppressed. We also investigate the scattering of light off graphene due to the plasmons in a periodic dielectric environment and we find that the plasmon resonance separates in two peaks corresponding to the forward and backward plasmon modes. The narrower linewidth of the forward propagating plasmon may be of interest for refractive index sensing and the DC current control could be used for the modulation of mid-infrared electromagnetic radiation.

Abstract. We theoretically demonstrate a high-sensitivity, graphene-plasmon based refractive index sensor working in the mid-infrared at room temperature. The bulk figure of merit of our sensor reaches values above 10, but the key aspect of our proposed plasmonic sensor is its surface sensitivity which we examine in detail. We have used realistic values regarding doping level and electron relaxation time, which is the limiting factor for the sensor performance. Our results show quantitatively the high performance of graphene-plasmon based refractive index sensors working in the mid-infrared.

We theoretically investigate under which conditions nonlocal plasmon response in monolayer graphene can be detected. To this purpose, we study optical scattering off graphene plasmon resonances coupled using a subwavelength dielectric grating. We compute the graphene conductivity using the Random Phase Approximation (RPA) obtaining a nonlocal conductivity and we calculate the optical scattering of the graphene-grating structure. We then compare this with the scattering amplitudes obtained if graphene is modeled by the local RPA conductivity commonly used in the literature. We find that the graphene plasmon wavelength calculated from the local model may deviate up to $20\%$ from the more accurate nonlocal model in the small-wavelength (large-$q$) regime. We also find substantial differences in the scattering amplitudes obtained from the two models. However, these differences in response are pronounced only for small grating periods and low temperatures compared to the Fermi temperature.Comment: Accepted for publication in Physical Review B. 15 pages, 9 figure

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We theoretically investigate graphene plasmons in the presence of a low density of adatoms on the graphene surface. The adatoms can significantly modify the conductivity and plasmonic properties of graphene and may produce a level splitting with the plasmon mode, resulting in two plasmon branches. The high energy branch exhibits large losses and the low energy branch exhibits low losses. Our model may also be considered as a simple model for molecules on graphene and we show that graphene plasmons are sensitive to such changes in the environment. Our microscopic treatment of plasmons and adatoms shows the sensitivity of plasmons and highlights the potential of graphene plasmons for sensing purposes.