Formation Filling Factor of 2D Wigner Crystal and the Competition with Interlayer Interaction*

In unbalanced bilayer 2D electron systems with different interlayer distances, we find that the filling factor for the formation of the Wigner crystal in the dilute layer is influenced by the presence of the adjacent high-density layer. Our measurements reveal that electrons are transferred between the two layers as a function of increasing magnetic field. Once the field reaches a sufficiently high value, the Wigner crystal forms at a critical filling factor of the dilute layer, and then the layer densities remain constant at higher fields. We find that this critical formation filling factor is significantly smaller than the value for single-layer Wigner crystal (1/5), and shows a strong dependence on the interlayer distance and layer densities. The data highlight the competition between the intra-layer and inter-layer interactions.