The Cyclotron Spin-Flip Mode as the Lowest-Energy Excitation of   Unpolarized Integer Quantum Hall States
  The cyclotron spin-flip modes of spin unpolarized integer quantum Hall states ($\nu =2,4$) have been studied with inelastic light scattering. The energy of these modes is significantly smaller compared to the bare cyclotron gap. Second order exchange corrections are held responsible for a negative energy contribution and render these modes the lowest energy excitations of unpolarized integer quantum Hall states. 
L.V. Kulik, I.V. Kukushkin, S. Dickmann, V.E. Kirpichev, A.B. Van'kov,   A.L. Parakhonsky, J.H. Smet, K. von Klitzing, W. We...