The giant negative magnetoresistance in two-dimensional electron gases

The giant negative magnetoresistance (GNMR), observed in two-dimensional electron gases of high mobility, is studied by controlled definition of additional short range scatterers in form of two-dimensional Lorentz arrays of varying obstacle density, as well as in the presence of edge scattering. The results support models which ascribe the temperature-independent regime of the GNMR to strong, classical scattering and the temperature-dependent regime to electron-electron interactions under the influence of mixed disorder. The threshold magnetic field, which separates the two regimes, is in rough agreement with the lower percolation transition of the Lorentz array. At large obstacle densities, interaction corrections are suppressed and memory effects like retroreflection and skipping-orbit transport become more relevant. Shape, amplitude and width of the GNMR depend sensitively on the time scales of the contributing scattering mechanisms, which comprise short- and long-range scattering at defects as well as scattering at the sample edges and at phonons. This interplay can lead to qualitatively similar shapes for quite different parameter values.