HOPPING TRANSPORT IN A MAGNETIC-FIELD - KADANOFF-BAYM-KELDYSH APPROACH AND MAGNETOCONDUCTIVITY

The rate equations for hopping transport in strongly disordered systems in the presence of electric and magnetic fields of any strength are rederived and generalized by using the Green-function technique of Kadanoff, Baym, and Keldysh. On the basis of the resulting equations, which are linearized with respect to the electric field, the magnetoconductivity is studied numerically and in the variable-range-hopping regime also by means of effective-medium theory. In contrast to other authors, we find that, similarly as in the nearest-neighbor-hopping regime, the magnetoconductivity in the variable-range-hopping regime changes its sign by changing from electronlike to holelike transport, at least at low magnetic fields. © 1995 The American Physical Society.