EFFECTIVE-MEDIUM METHOD FOR HOPPING TRANSPORT IN A MAGNETIC-FIELD

An effective-medium theory for studying the influence of a magnetic fi eld on hopping transport has been developed. It permits both the magne toconductivity and the Hall effect to be studied in the nearest-neighb or-hopping (NNH) and in the variable-range-hopping (VRH) regime. The m ethod has been applied to the de and ac Hall effect in three-dimension al systems. For NNH the static Hall mobility proves to be exponentiall y small in the critical hopping length. This fact results in a change of the sign of the Hall mobility of intermediate frequencies. For VRH the de Hall mobility exhibits a powerlike dependence on temperature. O wing to this fact the Hall mobility is nearly independent of frequency for small frequencies.