Anomalous g-factor in a Si/SiGe heterostructure with oscillatory Ge concentration

We measure an electron g-factor of 1.6 in a quantum well consisting of predominately silicon with an oscillating varying concentration of Ge that oscillates in space between 0% and 9% with a period of 1.8 nm.  This result is surprising, because bulk materials at all compositions of

Si_x Ge_1-x in this range have g-factors very close to 2.  This unexpected g-factor is a sign that strong spin-orbit coupling is present in this quantum well, which has been shown to host quantum dots andwith have large valley splitting [1], and which is useful for electrically-driven electron spin resonance.  We hypothesize that the high spatial frequency changes in Ge concentration present in this sample lead to contributions to the electronic states from points in the Brillouin zone far from the conduction band minimum –regions that play very little role in the physics of conventional, pure-Si quantum wells.