Electronic transport in ultrahigh-conductivity aligned carbon nanotube assemblies

Macroscopic assemblies of aligned carbon nanotubes (CNTs) with ultrahigh conductivity (> 10 MS/m) have recently emerged. They are promising for replacing copper- or aluminum-based electrical cables, but further conductivity improvement requires a microscopic understanding of electronic transport processes in CNT assemblies. In particular, it is of great importance to elucidate the roles of disorder, doping, and electron-electron interactions in determining the conductivity. Here, we describe our temperature- and magnetic field-dependent conductivity measurements on aligned CNT fibers and bundles produced by the solution spinning method. We observed a metallic behavior in a wide temperature range (30–300 K), i.e., conductivity monotonically increasing with decreasing temperature. At low temperatures (< 50 K), strongly temperature-dependent negative magnetoresistance appeared, a hallmark of weak localization, suggesting quantum coherent transport. We determined the dimensionality and coherence lengths of carriers via analysis of the weak localization behavior. In addition to macroscopic CNT fibers with diameters of ∼10 μm, we also conducted conductivity measurements on individual crystalline CNT bundles (with diameters ∼ 50 nm and lengths ∼ 30 μm) that constitute the fibers.