2 7 N ov 1 99 9 A possible role of D − band in hopping conductivity and metal - insulator transition in 2 D structures

A simple two-band model is suggested explaining recently reported unusual features for hopping magnetoresistance and the metal-insulator transition in 2D structures. The model implies that the conductivity is dominated by the upper Hubbard band (D-band). Experimental studies of hopping magnetoresistance for Si δ-doped GaAs/AlGaAs heterostructure give additional evidences for the model.