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Observation of a transient decrease in terahertz conductivity of single-layer graphene induced by ultrafast optical
Giriraj Jnawali1, Yi Rao, Hugen Yan
1Department of Physics, Columbia University, New York, New York 10027, USA.
Nano Letters
|January 22, 2013
Summary
We measured terahertz conductivity in graphene, finding photoexcitation decreases conductivity by increasing carrier scattering. This behavior in single-layer graphene differs from previous studies and is linked to nonequilibrium conditions.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Optoelectronics
Background:
- Single-layer graphene exhibits unique electronic properties.
- Terahertz (THz) spectroscopy is crucial for probing carrier dynamics in materials.
- Understanding photoinduced effects in graphene is key for optoelectronic applications.
Purpose of the Study:
- To measure the terahertz frequency-dependent conductivity of graphene.
- To investigate the transient photoresponse of graphene after optical excitation.
- To elucidate the mechanisms behind the observed photoconductivity.
Main Methods:
- Terahertz frequency-dependent sheet conductivity measurements.
- Femtosecond optical pump-probe spectroscopy.
- Analysis using the Drude model.
Main Results:
- Unexcited graphene showed a strong free-carrier response, consistent with the Drude model (carrier scattering time of 70 fs).
- Photoexcitation resulted in a transient decrease in graphene conductivity.
- The photoresponse, while differing in frequency dependence, is Drude-like, attributed to increased carrier scattering.
Conclusions:
- The negative photoconductive response in chemical vapor deposition-grown graphene is due to increased carrier scattering, not carrier density changes.
- This behavior is characteristic of high-mobility, doped graphene samples.
- The photoinduced conductivity transient has a picosecond lifetime, indicating nonequilibrium excitation.
