High-field terahertz response of graphene

M J Paul¹, Y C Chang², Z J Thompson¹, A Stickel¹, J Wardini¹, H Choi³, E D Minot¹, T B Norris^2,4 and Yun-Shik Lee¹

tnorris@umich.edu                            
¹ Department of Physics, Oregon State University, Corvallis, OR 97331, USA
² Center for Ultrafast Optical Science and Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI 48109, USA
³ School of Electrical and Electronic Engineering, Yonsei University, Seoul, Republic of Kore
a

http://m.iopscience.iop.org/1367-2630/15/8/085019
We investigate the response of multi-layer epitaxial graphene and chemical vapor deposition (CVD)-grown single-layer graphene to strong terahertz (THz) fields. Contrary to theoretical predictions of strong nonlinear response, the transmitted fields exhibit no harmonic generation, indicating that the nonlinear response is limited by fast electron thermalization due to carrier–carrier scattering. The fast electron heating gives rise to large THz transmission enhancement (> 15%) in single-layer CVD graphene at high THz fields (E_THz > 10 kV cm⁻¹). The nonlinear effects exhibit non-Drude behavior in the THz conductivity, where THz fields induce extreme non-equilibrium electron distributions

Abstract-Terahertz transmission ellipsometry of vertically aligned multi-walled carbon nanotubes

http://apl.aip.org/resource/1/applab/v101/i11/p111107_s1?isAuthorized=no

M. J. Paul¹, N. A. Kuhta¹, J. L. Tomaino¹, A. D. Jameson¹, L. P. Maizy¹, T. Sharf¹, N. L. Rupesinghe², K. B. K. Teo², S. Inampudi³, V. A. Podolskiy³, E. D. Minot¹, and Yun-Shik Lee¹

¹Department of Physics, Oregon State University, Corvallis, Oregon 97331-6507, USA
²AIXTRON Ltd., Buckingway Business Park, Anderson Road, Swavesey, Cambridge CB24 4FQ, United Kingdom
³Department of Physics and Applied Physics, University of Massachusetts Lowell, Lowell, Massachusetts 01854, USA 

We demonstrate time-resolved terahertz transmission ellipsometry of vertically aligned multi-walled carbon nanotubes. The angle-resolved transmission measurements reveal anisotropic characteristics of the terahertz electrodynamics in multi-walled carbon nanotubes. The anisotropy is, however, unexpectedly weak: the ratio of the tube-axis conductivity to the transverse conductivity, σ_z/σ_xy ≅ 2.3, is nearly constant over the broad spectral range of 0.4–1.6 THz. The relatively weak anisotropy and the strong transverse electrical conduction indicate that THz fields readily induce electron transport between adjacent shells within multi-walled carbon nanotubes.

© 2012 American Institute of Physics