5 research outputs found
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