Far- and mid-infrared anisotropy of magnetically aligned single-wall carbon nanotubes studied with synchrotron radiation

We performed polarized infrared reflectivity measurements on magnetically oriented carbon nanotubes using conventional light sources as well as synchrotron radiation. A strong anisotropy in the far-infrared spectral range was found, indicating preferred orientation of metallic tubes. Much less effect is seen in the spectral region typical of semiconducting tubes. We propose an explanation based on preferred orientation of metallic tubes, polarization-dependent dipole selection rules, and possible doping effects in these materials.