Metamorphosis of a quantum Hall bilayer state into a composite fermion metal

Composite fermion (CF) metal states emerge in quantum Hall bilayers at total Landau level filling factor ν T = 1 when the tunneling gap collapses by application of in-plane component of the magnetic field. Evidence of this transformation is found in the continua of spin excitations observed by inelastic light scattering below the spin-wave mode at the Zeeman energy. The low-lying spin modes are interpreted as quasiparticle excitations with simultaneous changes in spin orientation and composite fermion Landau level index. The results highlight significant differences of bilayer CF quasiparticles from those in single layers.