Spin-orbit enhancement in Si/SiGe heterostructures with oscillating Ge concentration

Abstract

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. We also provide a detailed explanation for this resonance phenomenon. This 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. 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. Indeed, our calculations yield a Rabi frequency Ω Rabi /B > 500 MHz/T near the optimal Ge oscillation wavelength λ = 1.57 nm