Exploring an Independent Contact Scheme in Si/SiGe Bilayers for studies of spontaneous interlayer coherence.

We detail the fabrication and low-temperature magneto-transport measurements of an undoped Si/SiGe antisymmetric double quantum well heterostructure. Through a combination of top and bottom gates, this novel device architecture enables fully independent tuning of the electron density in both layers while allowing for the realization of independent contacts to each quantum well. Owing to enhanced device stability, integer quantum Hall states at various total filling factors are observed at both matched and mis-matched densities. These states arise from inter-layer effects; either through inter-layer coherence, or through the symmetric-antisymmetric tunneling gap. To disentangle these two mechanisms, the evolution of the filling fraction’s excitation gap is studied as a function of density, and compared to the single particle tunneling energy, Δ_SAS, obtained from Schrödinger-Poisson simulations. Both the onset of spontaneous interlayer coherence and an anomalous magnetic field dependence of valley splitting are discussed.