Seeing Dirac plasmons in graphene using infrared nano-imaging
We have applied antenna-based infrared (IR) nano-spectroscopy and nano-imaging to
investigate Dirac plasmons in monolayer graphene. This experimental technique
enables IR imaging with nano-scale spatial resolution, and also allows one to investigate
electromagnetic phenomena at wavevectors on the order of the Fermi wavevector in
gated graphene. Nano-spectroscopy and nano-imaging experiments have uncovered
rich optical effects associated with the Dirac plasmons of graphene [Nano Lett. 11, 4701
(2011)]. We were able to directly image Dirac plasmons propagating over sub-micron
distances [Nature 487, 82 (2012)]. We have succeeded in altering both the amplitude
and wavelength of these plasmons by gate voltage in common graphene/SiO2/Si back-
gated structures. We investigated losses in graphene using plasmon interferometry: by
exploring real space profiles of plasmon standing waves formed between the tip of our
nano-probe and edges of the samples. Plasmon dissipation quantified through this
analysis is linked to the exotic electrodynamics of graphene [Nature-Physics 4, 532
(2008), PRL 102, 037403 (2009)].
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