Terahertz Driven Ultrafast Photo-carrier Dynamics in Single-Layer Graphene

The unique electronic structure of Graphene gives rise to its remarkable electrical and optical properties such as high carrier mobility and strong absorption of electromagnetic waves over a broad spectral range, which suggest its promising application to ultra-highspeed photonic devices. We demonstrate extraordinary ultrafast carrier dynamics of optically excited photocarriers in single layer CVD-grown suspended graphene induced by strong THz fields. Both strong THz fields and photoexcitation enhance the THz transmission of graphene mainly due to the increase of carrier scattering rates. However, the relaxation of photocarriers show opposite effect of the THz fields and photoexcitation. Photoexcitation increases the relaxation time via the reabsorption of optical phonons by photocarriers, while strong THz fields reduce the relaxation time because the field induced redistribution of electrons opens up unoccupied states in the conduction band and consequently enhances the relaxation and the phonon emission.