VARIABLE-RANGE-HOPPING CONDUCTION IN LAC2, CEC2, OR GDC2 CRYSTALS ENCAPSULATED CARBON NANOCAGES

An experimental study of electrical transport phenomena in magnetic fi elds H up to 15 T in pressed samples of three porous systems composed of carbon nanocages in which LaC2, CeC2, or GdC2 crystals are encapsul ated is reported. The exp[(T-0/T)(1/3)] temperature dependence in the zero-field dc electrical resistance R(0) is found at low temperatures. Below 50, 50, and 35 K for the LaC2, CeC2, and GdC2 system, respectiv ely, transverse magnetoresistance (MR), [R(H)-R(0)]/R(0), is negative. In the weak field region (H<0.15 T), the negative MR is quadratic in H, and becomes Linear in the field range 0.15-0.5 T. The linear and ne gative MR shores T--1.04+/-0.10 temperature dependence. The temperatur e dependence of R(0) is described in terms of Mott's law for two-dimen sional variable range hopping (2D VRH) conduction. The low field magne totransport features support a predicted quantum interference effect o n 2D VRH conduction. (C) 1996 American Institute of Physics.