Tuning Photoinduced Terahertz Conductivity in Monolayer Graphene: Optical Pump Terahertz Probe Spectroscopy

Abstract

Optical pump-terahertz probe differential transmission measurements of as-prepared single layer graphene (AG)(unintentionally hole doped with Fermi energy $E_F$ at $\sim$180 meV), nitrogen doping compensated graphene (NDG) with $E_F$ $\sim$10 meV and thermally annealed doped graphene (TAG) are examined quantitatively to understand the opposite signs of photo-induced dynamic terahertz conductivity $\Delta \sigma$. It is negative for AG and TAG but positive for NDG. We show that the recently proposed mechanism of multiple generations of secondary hot carriers due to Coulomb interaction of photoexcited carriers with the existing carriers together with the intraband scattering can explain the change of photoinduced conductivity sign and its magnitude. We give a quantitative estimate of $\Delta \sigma$ in terms of controlling parameters - the Fermi energy $E_F$ and momentum relaxation time $\tau$. Further, the cooling of photoexcited carriers is analyzed using super-collision model which involves defect mediated collision of the hot carriers with the acoustic phonons, thus giving an estimate of the deformation potential.

arXiv comment23 pages, 11 figures

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• Radiative decay effects influence the local electromagnetic response of the monolayer graphene with surface corrugations in terahertz range
• Intrinsic and extrinsic effects on intraband optical conductivity of hot carriers in photoexcited graphene
• Ultrafast Hot-Carrier cooling in Quasi Freestanding Bilayer Graphene with Hydrogen Intercalated Atoms
• Ultrafast terahertz conductivity in epitaxial graphene nanoribbons: an interplay between photoexcited and secondary hot carriers
• Optical and Terahertz Response of Carbon Nanostructures
• Ultrafast modulation in a THz graphene-based flat absorber through negative photoconductivity