Observation of a Transient Decrease in Terahertz Conductivity of Single-Layer Graphene Induced by Ultrafast Optical Excitation

We have measured the terahertz frequency-dependent sheet conductivity and its transient response following femtosecond optical excitation for single-layer graphene samples grown by chemical vapor deposition. The conductivity of the unexcited graphene sheet, which was spontaneously doped, showed a st...

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Bibliographic Details
Published in:Nano letters 2013-02, Vol.13 (2), p.524-530
Main Authors: Jnawali, Giriraj, Rao, Yi, Yan, Hugen, Heinz, Tony F
Format: Article
Language:English
Subjects:
Carriers
Chemical vapor deposition (including plasma-enhanced cvd, mocvd, etc.)
Compatibility
Condensed matter: electronic structure, electrical, magnetic, and optical properties
Cross-disciplinary physics: materials science
rheology
Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures
Electronic transport in multilayers, nanoscale materials and structures
Exact sciences and technology
Excitation
Femtosecond
Fullerenes and related materials
diamonds, graphite
Graphene
Materials science
Methods of deposition of films and coatings
film growth and epitaxy
Nanostructure
Photoexcitation
Physics
Scattering
Specific materials
Spectra
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Summary:We have measured the terahertz frequency-dependent sheet conductivity and its transient response following femtosecond optical excitation for single-layer graphene samples grown by chemical vapor deposition. The conductivity of the unexcited graphene sheet, which was spontaneously doped, showed a strong free-carrier response. The THz conductivity matched a Drude model over the available THz spectral range and yielded an average carrier scattering time of 70 fs. Upon photoexcitation, we observed a transient decrease in graphene conductivity. The THz frequency-dependence of the graphene photoresponse differs from that of the unexcited material but remains compatible with a Drude form. We show that the negative photoconductive response arises from an increase in the carrier scattering rate, with a minor offsetting increase in the Drude weight. This behavior, which differs in sign from that reported previously for epitaxial graphene, is expected for samples with relatively high mobilities and doping levels. The photoinduced conductivity transient has a picosecond lifetime and is associated with nonequilibrium excitation conditions in the graphene.
ISSN:1530-6984
1530-6992
DOI:10.1021/nl303988q