Spin-lattice interaction in the quasi one-dimensional helimagnet   LiCu_2O_2
  The field dependence of the electron spin resonance in a helimagnet, LiCu_2O_2, was investigated for the first time. In the paramagnetic state a broad resonance line was observed corresponding to a g-factor of 2.3. In the critical regime around the paramagnetic to helimagnetic phase transition the resonance broadens and shifts to higher frequencies. A narrow signal is recovered at low temperature, corresponding to a spin gap of 1.5 meV in zero field. A comprehensive model of the magnons is presented, using exchange parameters from neutron scattering (T. Masuda et al,   Phys. Rev. B 72, 014405), and the spin anisotropy determined here. The role of the quantum fluctuations is discussed. 
L. Mih\'aly, B. D\'ora, A. V\'anyolos, H. Berger, L. Forr\'o