Interlayer Interaction between Fractional Quantum Hall and Wigner Crystal States in a Double Quantum Well System

We study a double quantum well structure consisting of two 22-nm-wide GaAs quantum wells separated by a 2-nm-wide AlAs barrier, with a total electron density of ~1×10¹¹ cm^-2. When the charge distribution is symmetric, the bilayer two-dimensional electron system exhibits a well-developed ν = 1/2 fractional quantum Hall state (FQHS), characterized by vanishing R_xx and a quantized R_xy plateau consistent with the Halperin (3,3,1) FQHS [1], which arises from the interlayer interaction between two ν = 1/3 FQH liquids. The ν = 1/2 state is surrounded by a bilayer Wigner crystal phase [2] -- an ordered electron solid stabilized by strong interlayer Coulomb interaction. Upon introducing a charge imbalance, both R_xx minimum and R_xy plateau gradually shift toward the lower filling factors, while the quantized R_xy value transitions from 2h/e² to 3h/e². As we further increase the imbalance, these features continue to move toward ν = 1/3, with the well-defined 3h/e² quantization persisting. These observations suggest the presence of intermediate states in which a ν = 1/3 FQHS in one layer is coupled to a Wigner crystal in the other layer through interlayer interaction.

References:

[1] J.P. Eisenstein et al., New Fractional Quantum Hall State in Double-Layer Two-Dimensional Electron Systems, Phys. Rev. Lett. 68, 1383 (1992).

[2] H.C. Manoharan et al., Evidence for a Bilayer Quantum Wigner Solid, Phys. Rev. Lett. 77, 1813 (1996).