High Field Terahertz Electron Dynamics in Optically excited Carbon Nanotubes

ORAL

Abstract

Carbon nanotubes (CNTs) have exceptional electrical and optical properties which have inspired unique applications in nanoscale optoelectronics. We present an experimental study demonstrating anisotropic nonlinear THz transmission in free standing multi-walled carbon nanotubes (MWNTs). Unidirectionally aligned free-standing MWNTs form a quasi-one-dimensional semi-metallic structure and exhibit highly anisotropic linear and nonlinear THz responses. Unlike a typical conducting medium in which strong THz pulses induce transparency, intense THz fields enhance absorption in MWNTs, which suggests that strong THz fields efficiently generate charge carriers in MWNTs. We carry out THz time-domain spectroscopy of the MWNT samples for the parallel polarization configuration. We obtain the complex refractive index of the MWNT samples analyzing the amplitude and phase spectra of the transmitted THz pulses and the results agree well with Drude model. Surprisingly, the THz induced absorption does not monotonically increase when the MWNTs are optically excited. THz fields induce transparency at intermediate field strengths (~600 kV/cm), indicating that exotic quantum effects such as resonant quantum tunneling govern the photocarrier dynamics in MWNTs.

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Authors

  • Ali Mousavian

    Department of Physics, Oregon State Univ

  • Kuo-Fu Tseng

    Idaho Accelerator Center, University of Oregon, Department of Physics, Oregon State Univ, University Of Oregon, Washington State University, Simon Fraser University, University of Southern Queensland, Australia, UC Davis, Oregon State University, Henan University

  • Kuo-Fu Tseng

    Idaho Accelerator Center, University of Oregon, Department of Physics, Oregon State Univ, University Of Oregon, Washington State University, Simon Fraser University, University of Southern Queensland, Australia, UC Davis, Oregon State University, Henan University

  • Kuo-Fu Tseng

    Idaho Accelerator Center, University of Oregon, Department of Physics, Oregon State Univ, University Of Oregon, Washington State University, Simon Fraser University, University of Southern Queensland, Australia, UC Davis, Oregon State University, Henan University

  • Kuo-Fu Tseng

    Idaho Accelerator Center, University of Oregon, Department of Physics, Oregon State Univ, University Of Oregon, Washington State University, Simon Fraser University, University of Southern Queensland, Australia, UC Davis, Oregon State University, Henan University

  • Yun-Shik Lee

    Department of Physics, Oregon State Univ, Oregon State Univ