Evidence and evaluation of the Bychkov-Rashba effect in SiGe/Si/SiGe quantum wells

Abstract

From spin resonance of two-dimensional (2D) conduction electrons in a modulation doped SiGe/Si/SiGe quantum well structure we find a 2D anisotropy of both the line broadening (dephasing time) and the g factor. Both can be explained consistently employing the Bychkov-Rashba (BR) term ${\mathcal{H}}_{\mathrm{BR}}=\ensuremath{\alpha}(\mathbf{k}\ifmmode\times\else\texttimes\fi{}\ensuremath{\sigma})\ensuremath{\cdot}{\mathbf{e}}_{z},$ which turns out here to be the dominant coupling between electron orbital motion and spin. We obtain a BR parameter of $\ensuremath{\alpha}=0.55\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}\mathrm{eV}\mathrm{}\mathrm{cm}$---three orders of magnitude smaller than in quantum well structures based on III-V semiconductors, consistent with the much smaller spin-orbit coupling in Si.