Quantum-Coherent Electron Transport in Carbon Nanotube Fibers and Bundles with Ultrahigh Conductivity

Macroscopic fibers of aligned carbon nanotubes (CNTs) with exceptional electrical conductivity (>10 MS/m) have emerged as potential alternatives to conventional metal-based electrical cables. However, to optimize their conductivity, a comprehensive understanding of the microscopic electronic transport processes within these CNT fibers is important, encompassing considerations of disorder, doping, and electron-electron interactions. This study presents the outcomes of temperature- and magnetic field-dependent conductivity measurements performed on solution-spun aligned CNT fibers and bundles. At high temperatures, all examined fiber and bundle samples exhibited metallic behavior, with conductivity increasing monotonically as the temperature was reduced from room temperature to a sample-specific temperature between 30 and 100 K. Below this characteristic temperature, the conductivity exhibited a gradual decrease with further decreases in temperature. Additionally, pronounced negative magnetoresistance manifested at low temperatures, signifying the presence of weak localization—a hallmark of quantum coherence in electron transport. Furthermore, investigations on individual bundles exfoliated from the fibers revealed fluctuations in conductivity as a function of magnetic field at temperatures below 50 K. These fluctuations, recognized as universal conductance fluctuations, provide further substantiation of the quantum-coherent nature of electron transport in the examined CNT bundles. By unraveling the interdependencies between temperature, magnetic field, and conductivity in CNT fibers and bundles, this study enhances our understanding of quantum-coherent electron transport phenomena, thereby contributing to the advancement of ultrahighly conductive materials for prospective applications.