Density dependence of the excitation gaps in an undoped Si/SiGe double-quantum-well heterostructure

Abstract

We report low-temperature magneto-transport measurements of an undoped Si/SiGe asymmetric double quantum well heterostructure. The density in both layers is tuned independently utilizing a top and a bottom gate, allowing the investigation of quantum wells at both imbalanced and matched densities. Integer quantum Hall states at total filling factor ${\nu }_{\text{T}}=1$ and ${\nu }_{\text{T}}=2$ are observed in both density regimes, and the evolution of their excitation gaps is reported as a function of density. The ${\nu }_{\text{T}}=1$ gap evolution departs from the behavior generally observed for valley splitting in the single layer regime. Furthermore, by comparing the ${\nu }_{\text{T}}=2$ gap to the single particle tunneling energy, ${\Delta }_{\text{SAS}}$, obtained from Schrödinger-Poisson (SP) simulations, evidence for the onset of spontaneous inter-layer coherence (SIC) is observed for a relative filling fraction imbalance smaller than $\sim 50\%$

6 pages, 3 figures, accepted in APL

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