Hopping Conductivity in a Single-Walled Carbon Nanotube Network

We investigate the resistance and magnetoresistance (MR) of an entangled single-walled carbon nanotube (SWNT) network. The temperature dependence of conductance is fitted by formula G(T)=G₀exp-(T₀/T)^1/2 with T₀=15.8K at a wide temperature range from 4K to 300K. The MR defined by R(T,H)-R(T,0)/R(T,0) as a function of temperature and magnetic field perpendicular to the tube axis is negative at low temperatures. The MR amplitude increases as the temperature decreases at relative high temperature, but becomes decrease when temperature below 4K. The results are explained in terms of the coherent hopping of carriers in the presence of a Coulomb gap at low temperature.