Absorption spectroscopy in electron double layers: evidence for broken symmetry states

Optical absorption spectroscopy has been used to explore the phase diagram of the double layer electron system at v = 1. Absorption spectroscopy is shown to be sensitive to the evolution of the electron system from a regime in which a gap in the single-particle tunneling spectrum accounts for the quantized Hall state to a regime of weak tunneling in which inter-layer Coulomb interactions determine the nature of the excitation gap. Qualitative differences in magnetic field and temperature dependence of spectra are observed depending on the relative size of the single-particle tunneling gap, Most intriguingly, our measurements of samples in the regime of weak tunneling do not display a quenching of absorption intensity at v - 1 characteristic of the quantum Hall effect. (C) 2000 Elsevier Science B.V. All rights reserved.