Zero-Momentum Cyclotron Spin-Flip Mode in a Spin-Unpolarized Quantum   Hall System
  We report on a study of the zero-momentum cyclotron spin-flip excitation in the V=2 quantum Hall regime. Using the excitonic representation the excitation energy is calculated up to the second order Coulomb corrections. A considerable negative exchange shift relative to the cyclotron gap is established for cyclotron spin-flip excitations in the the spin-unpolarized electronic system. Under these conditions this type of states presents the {\it lowest-energy} excitations. For a fixed filling factor V=2 the energy shift is independent of the magnetic field which is in agreement with recent experimental observations. 
S. Dickmann and I.V. Kukushkin