Spin-orbit enhancement and g-factor renormalization in Si/SiGe heterostructures with oscillating Ge concentration*

We show that Ge concentration oscillations within the quantum well region of a Si/SiGe heterostructure can significantly enhance the spin-orbit coupling of the low-energy conduction-band valleys. Specifically, we find that for Ge oscillation wavelengths near λ = 1.57 nm a Dresselhaus spin-orbit coupling is produced that is over an order of magnitude larger than what is found in conventional Si/SiGe heterostructures without Ge concentration oscillations. Furthermore, enhanced inter-subband spin-orbit coupling leads to significant g-factor renormalization, creating a difference of ~ 0.01-0.04 between the g-factors of the ground and excited valleys for appropriate Ge oscillation wavelength and magnetic field direction. We provide an explanation for these enhancements, which involves the Ge concentration oscillations producing wavefunction satellite peaks a distance 2π/λ away in momentum space from each valley, which then couple to the opposite valley through Dresselhaus spin-orbit coupling. We also explore how the spin-orbit enhancement and g-factor renormalization can be exploited for qubit manipulation. For example, our results indicate that the enhanced spin-orbit coupling can enable fast spin manipulation within Si quantum dots using electric dipole spin resonance in the absence of micromagnets with Rabi frequencies of 100s of MHz.