Critical filling factor for the formation of a quantum Wigner crystal screened by a nearby layer

One of the most fascinating ground states of an interacting electron system is the so-called Wigner crystal where the electrons, in order to minimize their repulsive Coulomb energy, form an ordered array. Here, we report measurements of the critical filling factor (νC) below which a magnetic-field-induced, quantum Wigner crystal forms in a dilute, two-dimensional electron layer when a second, high-density electron layer is present in close proximity. The data reveal that the Wigner crystal forms at a significantly smaller νC compared to the νC (≃0.20) in single-layer two-dimensional electron systems. The measured νC exhibits a strong dependence on the interlayer distance, reflecting the interaction and screening from the adjacent, high-density layer.