Closing the gap between spatial and spin dynamics of electrons at the metal-to-insulator transition

We combine extensive precision measurements of the optically detected spin dynamics and magneto-transport measurements in a contiguous set of n-doped bulk GaAs structures in order to unambiguously unravel the intriguing but complex contributions to the spin relaxation at the metal-to-insulator transition (MIT). Just below the MIT, the interplay between hopping induced loss of spin coherence and hyperfine interaction yields a maximum spin lifetime exceeding 800~ns. At slightly higher doping concentrations, however, the spin relaxation deviates from the expected Dyakonov-Perel mechanism which is consistently explained by a reduction of the effective motional narrowing with increasing doping concentration. The reduction is attributed to the change of the dominant momentum scattering mechanism in the metallic impurity band where scattering by local conductivity domain boundaries due to the intrinsic random distribution of donors becomes significant. Here, we fully identify and model all intricate contributions of the relevant microscopic scattering mechanisms which allows the complete quantitative modeling of the electron spin relaxation in the entire regime from weakly interacting up to fully delocalized electrons

Influence of oval defects on transport properties in high-mobility two-dimensional electron gases

Rare macroscopic growth defects next to a two-dimensional electron gas influence transport properties and cause a negative magnetoresistance. On the basis of this, we show that the number of oval defects seen on the material surface is comparable with the density of macroscopic growth defects determined from the negative magnetoresistance. We examine several materials with different densities of oval defects n(S) which were grown in one cycle under the same conditions to verify our observations. Paradoxically, the material with the largest number of oval defects has also the highest electron mobility. (C) 2016 AIP Publishing LLC