Time resolved terahertz spectroscopy of low frequency electronic resonances, and optical pump-induced terahertz photoconductivity in reduced graphene oxide membrane

Srabani Kar (1, 2) , Swetha Jayanthi (3) , Eric Freysz (4) , Ajay Kumar Sood (1, 2)

1 Department of Physics [Bangalore]
2 Center for Ultrafast Laser Applications
3 Center for Nano Science and Engineering
4 LOMA - Laboratoire Ondes et Matière d'Aquitaine

Towards ultrafast optoelectronic applications of single and a few layer reduced graphene oxide (RGO), we study time domain terahertz spectroscopy and optical pump induced changes in terahertz conductivity of self-supported RGO membrane in the spectral window of 0.5–3.5 THz. The real and imaginary parts of conductivity spectra clearly reveal low frequency resonances, attributed to the energy gaps due to the van Hove singularities in the density of states flanking the Dirac points arising due to the relative rotation of the graphene layers. Further, optical pump induced terahertz conductivity is positive, pointing to the dominance of intraband scattering processes. The relaxation dynamics of the photo-excited carriers consists of three cooling pathways: the faster (∼450 fs) one due to optical phonon emission followed by disorder mediated large momentum and large energy acoustic phonon emission with a time constant of a few ps (called the super-collision mechanism) and a very large time (∼100 ps) arising from the deep trap states. The frequency dependence of the dynamic conductivity at different delay times is analyzed in term of Drude-Smith model.

Mots clés: TeraHertz spectroscopy

Domaines: Optique [physics.optics]

Srabani Kar, Swetha Jayanthi, Eric Freysz, Ajay Kumar Sood. Time resolved terahertz spectroscopy of low frequency electronic resonances, and optical pump-induced terahertz photoconductivity in reduced graphene oxide membrane. Carbon, 2014, 80, pp.762-770. ⟨10.1016/j.carbon.2014.09.030⟩. ⟨hal-01094641⟩