Magnetic field dependence of the metal–insulator transition in Ga[Al]As-heterostructures

A metal–insulator transition at zero magnetic field is observed in Ga[Al]As-heterostructures where a high density of self-assembled InAs-quantum dots is located in the region of the two-dimensional electron gas (2DEG). This transition occurs only in samples with high dot densities. In contrast to other two-dimensional systems showing a metallic phase the Coulomb energy is comparable to the kinetic energy in our systems. Measurements in perpendicular fields reveal that the resistivity at B=0 is composed of several contributions. In the metallic regime a weak localization peak is superposed on top of a broad negative magnetoresistivity. In the insulating regime, the weak localization peak at B=0 develops into a very pronounced negative magnetoresistivity with decreasing electron density. Pronounced, almost B-periodic oscillations in the magnetoresistivity are observed in addition to universal conductance fluctuations.