Metal-insulator transition in doped single-wall carbon nanotubes

Abstract

We find strong evidence for a metal-insulator (MI) transition in macroscopic single wall carbon nanotube conductors. This is revealed by systematic measurements of resistivity and transverse magnetoresistance (MR) in the ranges 1.9-300 K and 0-9 Tesla, as a function of p-type redox doping. Strongly H 2 SO 4 -doped samples exhibit small negative MR, and the resistivity is low and only weakly temperature dependent. Stepwise de-doping by annealing in vacuum induces a MI transition. Critical behavior is observed near the transition, with ρ(T) obeying power-law temperature dependence, ρ(T) ∝ T -β . In the insulating regime (high annealing temperatures) the ρ(T) behavior ranges from Mott-like 3-dimensional (3D) variable-range hopping

Pressure-Induced Transition in Magnetoresistance of Single-Walled Carbon Nanotubes

“…From 0 to 1.0 GPa the MR curves roughly collapse with each other, showing a nonmonotonic dependence on B and changing from negative to positive at 2 T. This agrees well with the previous measurements [18,19] at ambient pressure. The negative-to-positive MR transition with increasing field was suggested to be induced by the field modified electron density of states (DOS) or by a metal-semiconductor transition [19]. Under high pressures (5.5-11.4 GPa) the MR curves roughly collapse with each other onto another trend, decreasing monotonically with increasing field.…”

“…However, we cannot rule out completely other possible mechanisms. For example, a pressure-induced metalinsulator transition similar to the doping effect, might cause a MR transition in high fields as shown by Vavro et al [19]. We also tried to fit the data with a 3DWL model, but the agreement is much worse.…”

Correlation of properties with preferred orientation in coagulated and stretch-aligned single-wall carbon nanotubes

“…Both are consequences of disorder. The low-T CD-VRH regime indicates the opening of a small gap ∆ c in the density of states when ∆ c > kT, signifying a metal-insulator transition [10]. In contrast, the thermal conductivity is insensitive to the presence of PVA, the T dependence being dominated by the heat capacity as is generally observed [11].…”

Cotunneling and one-dimensional localization in individual disordered single-wall carbon nanotubes: Temperature dependence of the intrinsic resistance

“…4,[11][12][13][14] In our experiments, the intrinsic resistance of disordered SWNT's is measured in a four-point configuration. 15 The intrinsic resistance is found to be thermally activated.…”