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Exciting Plasmons Print
Wednesday, 07 December 2011 17:01

Researchers at the University of California, Berkeley and the ALS have used the far/mid-infrared FTIR of ALS Beamline 1.4 to study the plasmon excitation in graphene. They observed remarkably strong and tunable plasmon excitations in the Terahertz range, which demonstrate the exotic behaviour of 2D massless Dirac electrons and shed new light on graphene's application in THz metamaterials.

Plasmons describe collective oscillations of electrons and play a fundamental role in dynamic responses of electron systems and form the basis of research into optical metamaterials. Researchers explore plasmon excitations in engineered graphene micro-ribbon arrays by detecting the transmission of polarized light with THz frequencies. They observed plasmon resonances with remarkably large oscillator strengths, as manifest in prominent room-temperature optical absorption peaks. Also, they demonstrated that graphene plasmon resonances can be tuned over a broad terahertz frequency range by changing the micro-ribbon width and in situ electrostatic doping.

feng plasmons

(a) Side view of the graphene-based device in the experiment. (b) AFM image of graphene micro-ribbon array. (c) Plasmon absorption spectrum of graphene micro-ribbon array in the THz range(1THz=33.3cm-1) .  Over 13% of incident light is absorbed by the atomically thick graphene ribbon array.  (d) Scaling laws of plasmon frequency as a function of charge density and ribbon width. Solid lines represent the scaling law obeyed by massless electrons in graphene. Dash lines represent  that of ordinary massive electrons.

This combination of electrical tuning and structural engineering in one material makes graphene a truly unique platform for plasmonic metamaterials. The observed unusual scaling behavior of plasmon frequency with ribbon width and carrier concentration also bears the signature to 2D Dirac electrons in graphene. The results represent a first look at light-plasmon coupling in graphene and point to potential graphene-based terahertz metamaterials.

 


 

Work performed on ALS Beamline 1.4.4

Citation: L. Ju, B. Geng, J. Horng, Caglar Girit, Michael Martin, Zhao Hao, Hans A. Bechtel, Xiaogan Liang, Alex Zettl , Y. Ron  Shen, and F. Wang. “Graphene Plasmonics for Tunable Terahertz Metamaterials” Nat. Nanotechnology 6, 630-634 (2011).