Transport and magnetic properties in multi-walled carbon nanotube ropes: Evidence for superconductivity above room temperature

Abstract

Detailed analyses are made on previously published data for multi-walled carbon nanotubes. The field dependence of the Hall voltage, the temperature dependence of the Hall coefficient, and the magnetoresistance effect (Phys. Rev. Lett. 72, 697 (1994)) can all be consistently explained in terms of the coexistence of physically separated tubes and Josephson-coupled superconducting tubes with superconductivity above room temperature. The observed temperature dependencies of the remnant magnetization, the diamagnetic susceptibility, and the conductance are consistent with superconductivity above room temperature, but are inconsistent with ferromagnetic contamination. We also interpret the paramagnetic signal and unusual field dependence of the magnetization at 300 K (Phys. Rev. B 49, 15122 (1994)) as arising from the paramagnetic Meissner effect in a multiply connected superconducting network.