Evidence of interlayer correlation in spin excitations of quantum Hall bilayers with negligible tunneling

Manifestations of interlayer excitonic coherence in a quantum Hall bilayer with negligible tunneling occur in low-lying spin excitations measured by inelastic light scattering. The observation of quasiparticle spin-flip excitations with energies below the Zeeman gap identifies a composite-fermion metal as the high-temperature phase of the quantum Hall coherent state. Spin-flip intensities enable the determination of a critical temperature for this transformation that is in general agreement with those obtained from charge transport experiments.