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Ultrafast and nanoscale plasmonic phenomena in exfoliated graphene revealed by infrared pump-probe nanoscopy

  • Author(s): Wagner, M
  • Fei, Z
  • McLeod, AS
  • Rodin, AS
  • Bao, W
  • Iwinski, EG
  • Zhao, Z
  • Goldflam, M
  • Liu, M
  • Dominguez, G
  • Thiemens, M
  • Fogler, MM
  • Castro Neto, AH
  • Lau, CN
  • Amarie, S
  • Keilmann, F
  • Basov, DN
  • et al.

Published Web Location

https://doi.org/10.1021/nl4042577
Abstract

Pump-probe spectroscopy is central for exploring ultrafast dynamics of fundamental excitations, collective modes, and energy transfer processes. Typically carried out using conventional diffraction-limited optics, pump-probe experiments inherently average over local chemical, compositional, and electronic inhomogeneities. Here, we circumvent this deficiency and introduce pump-probe infrared spectroscopy with ∼20 nm spatial resolution, far below the diffraction limit, which is accomplished using a scattering scanning near-field optical microscope (s-SNOM). This technique allows us to investigate exfoliated graphene single-layers on SiO2at technologically significant mid-infrared (MIR) frequencies where the local optical conductivity becomes experimentally accessible through the excitation of surface plasmons via the s-SNOM tip. Optical pumping at near-infrared (NIR) frequencies prompts distinct changes in the plasmonic behavior on 200 fs time scales. The origin of the pump-induced, enhanced plasmonic response is identified as an increase in the effective electron temperature up to several thousand Kelvin, as deduced directly from the Drude weight associated with the plasmonic resonances. © 2014 American Chemical Society.

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