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Bulk samples of carbon multilayer nanotubes with the structure of nestedcones (fishbone structure) suitable for transport measurements, were preparedby compressing under high pressure (~25 kbar) a nanotube precursor synthesizedthrough thermal decomposition of polyethylene catalyzed by nickel. Thestructure of the initial nanotube material was studied using high-resolutiontransmission electron microscopy. In the low-temperature range (4.2 - 100 K)the electric resistance of the samples changes according to the law ln \rho ~(T_0/T)^{1/3}, where T_0 ~ 7 K. The measured magnetoresistance is quadratic inthe magnetic field and linear in the reciprocal temperature. The measurementshave been interpreted in terms of two-dimensional variable-range hoppingconductivity. It is suggested that the space between the inside and outsidewalls of nanotubes acts as a two-dimensional conducting medium. Estimatessuggest a high value of the density of electron states at the Fermi level ofabout 5 10^{21} eV^{-1} cm^{-3}.Comment: 8 pages, 4 figures. EM photographic images on figures 1a, 1b, 1c  attached as JPG files. For correspondence mail to tsebro@sci.lebedev.r

journal of experimental and theoretical physics

Temperature dependence of electric resistance and magnetoresistance of pressed nanocomposites of multilayer nanotubes with the structure of nested cones