Electron g-factor renormalization in SiGe superlattice quantum wells*

An electron g-factor of g ~ 1.6 has been observed in a SiGe superlattice quantum well with a periodic Ge concentration ranging from 0% to 9% within a supercell of length L ~ 1.8 nm. This shift from g_o = 2 represents a g-factor renormalization one to two orders of magnitude larger than what may be naively expected based on the material composition of the quantum well. We present a model that attributes this strong renormalization to the coupling of the conduction band minima to states with strong spin-orbit coupling.  More specifically, the periodic potential arising from the Ge concentration oscillations couples the conduction band minima near the X-point to states near the zone center of the Brillouin zone. In contrast to the conduction band minima, which have a spectral weight dominated by p_z orbitals, the states near the Brillouin zone center have significant contributions from all three p orbital species, which gives rise to strong spin-orbit coupling and g-factor renormalization. This g-factor renormalization may be useful in manipulation of qubit spin resonance without the use of micromagnets.