Giant negative magnetoresistance of a degenerate two-dimensional electron gas in the variable-range-hopping regime

We present an experimental study of magnetoresistance of a degenerate, two-dimensional electron gas with a broad range of localization length in the variable-range-hopping regime. At low magnetic fields, a giant negative magnetoresistance of R(0)/R(H){~}7 is observed and is confirmed to be an orbital mechanism in origin. At high fields, the two-dimensional electron gas shows a contrasting transport behavior of a positive magnetoresistance. We found the transition from negative to positive magnetoresistance is temperature independent and occurs at a magnetic field corresponding to the lowest Landau-level filling factor of {ν}=2. While we cannot reach a definite conclusion as to the origin of the giant negative magnetoresistance, our experimental data suggest the important role of the Landau-level quantization to the transport properties of a degenerate two-dimensional electron gas in the variable-range-hopping regime.