Thermoelectric power and thermal conductivity of single-walled carbon nanotubes

Abstract

We have measured the temperature-dependent thermopower (TEP) and thermal conductivity (κ) of bulk samples of single-walled nanotube (SWNT) bundles. The TEP of SWNT's approaches zero as T→0, indicating a metallic density of states at the Fermi level in spite of their non-metallic resistivity behavior. At moderate temperatures, the TEP is large and positive, while a single metallic tube should have electron-hole symmetry and thus a zero thermopower. The measured data can be fit using a model comprising hole-like metallic tubes and electron-like semiconducting tubes in parallel. The thermal conductivity of SWNT's is found to be large, and dominated by phonons at all temperatures. At low temperature, κ(T) is linear. The data can be fit by a single-scattering-time model; the model confirms that the low-temperature linear behavior is due to the thermal conductivity of a single one-dimensional phonon subband, and that the phonon mean free path is of order 100 nm.