Localization in random electron systems:AlxGa1−xAsalloys and intentionally disorderedGaAs∕AlxGa1−xAssuperlattices

Abstract

The localization properties of single-particle and collective excitations were investigated in ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ alloys and in intentionally disordered $\mathrm{Ga}\mathrm{As}∕{\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ superlattices by magnetoresistance and Raman scattering. It is shown that the Landau damping determines the localization length of the collective plasmonlike excitations in bulk ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ alloy, while the electrons are localized due to the alloy random potential. Meanwhile, the localization lengths of both the single-particle and collective excitations are limited by disorder in the intentionally disordered superlattices. In such a case, a comparison between the localization properties of the single-particle and collective excitations propagated in the same random potential is possible. The localization length of the individual electron is found to be considerably larger than the localization length of their collective excitations. This implies that the electron-electron interaction which is fundamental for the collective excitations increases localization. However, the difference between the localization of the single-particle and collective excitations decreases with the increasing disorder. Consequently, in clean electron systems the effect of the interaction on localization of elementary excitations is stronger. Additionally, a reasonable agreement has been found between the measured localization lengths for the single particle in the disordered superlattices and those numerically obtained from transfer matrix calculations.