Measurement of valley splitting in high-symmetry Si/SiGe quantum dots

We have demonstrated few-electron quantum dots in Si/SiGe and InGaAs, with occupation number controllable from N=0. These display a high degree of spatial symmetry and identifiable shell structure. Magnetospectroscopy measurements show that two Si-based devices possess a singlet N=2 ground state at low magnetic field, and therefore, the twofold valley degeneracy is lifted. The valley splittings in these two devices were 270 and 120 mu eV, suggesting the presence of atomically sharp interfaces in our heterostructures. (C) 2011 American Institute of Physics. [doi:10.1063/1.3569717]