  Resonant Rayleigh scattering of light from electrons confined in gallium
arsenide double quantum wells displays significant changes at temperatures that
are below one degree Kelvin. The Rayleigh resonance occurs for photon energies
that overlap a quantum well exciton and when electron bilayers condense into a
quantum-Hall state. Marked changes in Rayleigh scattering intensities that
occur in response to application of an in-plane magnetic field indicate that
the unexpected temperature dependence is linked to formation of non-uniform
electron fluids in a disordered quantum-Hall phase. These results demonstrate a
new realm of study in which resonant Rayleigh scattering methods probe quantum
phases of cold electrons in semiconductor heterostructures.
