Valley splitting in a Si/SiGe quantum point contact

We analyze transport data from a quantum point contact (QPC), fabricated on a modulation doped Si/SiGe heterostructure, to extract experimental estimates for the valley splitting. The experimental data are fit to a form derived from a valley coupling theory that takes into account the fact that the quantum well is grown on a miscut substrate. The results of the fitting analysis are compared to the results obtained by fitting to a simple phenomenological form; both methods indicate that electrostatic confinement and magnetic confinement enhance the valley splitting by reducing the lateral spatial extent of the electronic wavefunction. Consequently, the valley splitting can be much larger than the spin splitting for small magnetic fields. We observe different valley splittings for the two lowest orbital modes of the QPC, supporting the notion that when steps are present at the quantum well interface the spatial extent of the wavefunction plays a dominant role in determining the valley splitting.