WEAK LOCALIZATION AND ELECTRON ELECTRON INTERACTION IN MODULATION-DOPED GAAS/ALGAAS HETEROSTRUCTURES

Two MBE-grown GaAs/AlGaAs heterostructure wafers have been modified by helium ion implantation. Since implantation essentially only changes electron mobility, low-temperature experiments allowed the authors to study the quantum corrections to the electrical conductivity as a function of mobility. The first heterostructure wafer only had one electronic subband at the GaAs/AlGaAs interface populated. Weak localisation magnetoresistance was interpreted by a theory valid in a regime with only a few elastic scatterings during a time of phase coherence. At magnetic fields of the order of the inverse electron mobility, a quadratic magnetoresistance shows up in the experiments. Whereas they find that the temperature dependence of this conductivity correction is well in agreement with predicted effects of electron-electron interaction, the dependence on mobility is larger than any existing theory predicts, yet still in the region of the conductance quantum. The second heterostructure wafer had an electron density, which corresponded to a slight population of the second subband. The weak localisation magnetoresistance has for these samples a very unusual shape with 3 maxima. The authors interpret this behaviour as a result of a spin-orbit effect on the weak localisation in the upper subband induced by the interband scattering.