New polarization effect and collective excitation in S=1/2 quasi 1D   antiferromagnetic quantum spin chain
  Anomalous polarization characteristics of magnetic resonance in CuGeO3 doped with 2% of Co impurity are reported. For the Faraday geometry this mode is damped for the microwave field Bw aligned along a certain crystallographic direction showing that the character of magnetic oscillation differs from the standard spin precession. The observed resonance coexists with the ESR on Cu2+ chains and argued not to be caused by "impurity" EPR, as previously claimed, but to correspond to a previously unknown collective mode of magnetic oscillations in S=1/2 AF quantum spin chain. 
S.V.Demishev, A.V.Semeno, H.Ohta, S.Okubo, I.E.Tarasenko,   T.V.Ishchenko, N.E.Sluchanko