Abstract
Mono-sized ultra-small (0.4 nm in diameter) single-walled carbon nanotubes (SWNTs) were prepared by pyrolysis of tripropylamine molecules in the channels of porous zeolite AIPO(4)-5 (AFI) single crystals. These ultra-small nanotubes perhaps constitute the best example of one-dimensional (ID) quantum wires. Because these SWNTs are highly aligned and uniform in size, they show interesting electrical transport properties. Local density functional calculations indicate that when the diameter of the SWNT is smaller than 0.5 run, strong curvature effects induce strong sigma-pi mixing of the unoccupied orbitals. In this regime, metallicity can no longer be predicted by the simple band-folding picture, and these small-radius SWNTs generally have finite density of states at the Fermi level. Investigation of the magnetic and transport properties of these SWNTs revealed that at temperatures below 20 K, the 0.4nm tubes exhibit superconducting behavior manifest as an anisotropic Meissner effect, with a superconducting gap and fluctuation supercurrent. The measured superconducting characteristics display smooth temperature variations owing to one-dimensional fluctuations, with a mean-field superconducting transition temperature of 15 K. Statistical mechanic calculations based on the Ginzburg-Landau free energy functional yield predictions that are in excellent agreement with the experiments.