Variable range hopping conduction in multiwalled carbon nanotubes

An experimental study of electrical transport phenomena in magnetic-fields H up to 5 T in pressed samples of a porous system composed of multiwalled carbon nanotubes is reported. The exp[(T-0/T)(1/4)] temperature dependence in the zero-field de electrical resistance R(0) is found at low temperatures. Below 50 K, transverse magnetoresistance (MR), [R(H)-R(0)]/R(0), is negative. In the weak-field region (H<0.1 T), the negative MR is quadratic in H, and becomes linear in the field range 0.1-0.3 T. The linear and negative MR shows T-0.65+/-0.06 temperature dependence. The temperature dependence of R(0) is described in terms of Mott's law for three-dimensional variable range hopping (3D VRH) conduction. The low-held magnetotransport features support a predicted quantum interference effect on 3D VRH conduction. (C) 1998 American Institute of Physics.