Cyclotron spin-flip excitations in a \nu=1/3 quantum Hall ferromagnet
  Inelastic light scattering spectroscopy around the \nu=1/3 filling discloses a novel type of cyclotron spin-flip excitation in a quantum Hall system in addition to the excitations previously studied. The excitation energy of the observed mode follows qualitatively the degree of electron spin polarization, reaching a maximum value at \nu=1/3 and thus characterizing it as a \nu=1/3 ferromagnet eigenmode. Its absolute energy substantially exceeds the theoretical prediction obtained within the renowned single-mode approximation. Double-exciton corrections neglected utilizing the single-mode approach are evaluated within the framework of the excitonic representation and are inferred to be responsible for the observed effect. 
A.B.Van'kov (1), L.V.Kulik (1), S.M.Dickmann (1), I.V.Kukushkin (1 and   2), V.E.Kirpichev (1), W.Dietsche (2) and S.Schmult...