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Phonon sideband optical spectroscopy determines the energy of the dark K-momentum exciton for (6,5) carbon nanotubes. One-phonon sidebands appear in absorption and emission, split by two zone-boundary (K-point) phonons. Their average energy locates the E 11 K-momentum exciton 36 meV above the E 11 bright level, higher than available theoretical estimates. A model for exciton-phonon coupling shows the absorbance sideband depends sensitively on the K-momentum exciton effective mass and has minimal contributions from zone-center phonons, which dominate the Raman spectra of carbon nanotubes.

Magnetic alignment studies demonstrate that a fraction of acid purified single wall carbon nanotubes sSWNTsd exhibit both linear-orbital sdiamagnetic and/or paramagneticd and ferromagnetic sFMd anisotropies. The latter are unexpected, as prior studies have assumed that remaining FM impurities are encapsulated and play no role in SWNT alignment. The data imply a FM easy axis aligned with the nanotube, permit direct estimates of the FM moment size, and provide a more accurate measure of the SWNT magnetic anisotropy. In light of recent observations of FM proximity effects in nanotubes, our observation of attached or intrinsic FM anisotropy in these systems is an important consideration for future studies of carbon nanotube magnetism.

We find strong evidence for a metal-insulator sMId transition in macroscopic single wall carbon nanotube sSWNTd conductors. This is revealed by systematic measurements of resistivity and transverse magnetoresistance sMRd in the ranges 1.9‐300 K and 0‐9 Tesla, as a function of p-type redox doping. Strongly H2SO4-doped samples exhibit small negative MR, and the resistivity is low and only weakly temperaturedependent. Stepwise dedoping by annealing in vacuum induces a MI transition. Critical behavior is observed near the transition, with rsTd obeying a power-law temperature dependence, rsTd ~ T ˛b . In the insulating regime shigh annealing temperaturesd, the rsTd behavior ranges from Mott-like three-dimensional s3Dd variable-range hopping sVRHd, rsTd ~ expfsT0 / Td ˛1/4 g, to Coulomb-gap sCGVRHd behavior, rsTd ~ expfs˛T0 / Td ˛1/2 g. Concurrently, MRsBd becomes positive for large B, exhibiting a minimum at magnetic field Bmin. The temperature dependence of Bmin can be characterized by BminsTd = Bcs 1˛ T/ Tcd for a large number of samples prepared by different methods. Below a sample-dependent crossover temperature Tc, MRsBd is positive for all B. The observed changes in transport properties are explained by the effect of doping on semiconducting SWNTs and tube-tube coupling.