Evolution of the nu = 1 Ground-State in Coupled Double Quantum Wells:   Optical Evidence for Broken-Symmetry States
  We present the first magneto-absorption studies of coupled electron double layers in the quantum Hall regime. Optical absorption spectra in the vicinity of total filling factor nu = 1 reveal intriguing behavior that have no analog in the single electron layer nu = 1 state and demonstrate the interplay between single-particle tunneling and inter-layer Coulomb effects. The spectra provide direct evidence of a ground-state that evolves from a region dominated by single-particle tunneling to a regime in which inter-layer Coulomb interactions determine the nature of the ground-state. Moreover the spectra provide the first direct evidence that the incompressible ground-state at nu = 1 in the many-body regime is not fully pseudospin polarized and is sensitive to the effects of quantum fluctuations in the pseudospin variable. 
Michael J. Manfra (1), Justin C. Pniower (1), Bennett B. Goldberg (1),   Aron Pinczuk (2), Vittorio Pellegrini (3), Loren N....