Observation of collapse of pseudospin order in bilayer quantum Hall   ferromagnets
  The Hartree-Fock paradigm of bilayer quantum Hall states with finite tunneling at filling factor $\nu$=1 has full pseudospin ferromagnetic order with all the electrons in the lowest symmetric Landau level. Inelastic light scattering measurements of low energy spin excitations reveal major departures from the paradigm at relatively large tunneling gaps. The results indicate the emergence of a novel correlated quantum Hall state at $\nu$=1 characterized by reduced pseudospin order. Marked anomalies occur in spin excitations when pseudospin polarization collapses by application of in-plane magnetic fields. 
Stefano Luin, Vittorio Pellegrini, Aron Pinczuk, Brian S. Dennis,   Loren N. Pfeiffer, Ken W. West