Terahertz Transmission Ellipsometry of Vertically-Aligned Multi-Walled Carbon Nanotubes

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, ${\sigma _z } \mathord{\left/ {\vphantom {{\sigma _z } {\sigma _{xy} =2.3}}} \right. \kern-\nulldelimiterspace} {\sigma _{xy} =2.3}$, 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.