Finite-wavevector phonon coupling to degenerate electronic states in   LaSrCuO
  We consider finite-k electron-phonon coupling appropriate for a superconductor with a very short coherence length and local intersite pairs.   From group theoretical analyis we find that phonons with nonzero k can couple to degenerate electronic states in LaSrCuO and a Jahn-Teller-like distortion is found to be operative for E_u and E_g -symmetry O states. Experimentally observed anomalies in inelastic neutron scattering, ESR and EXAFS are found to be consistent with such an interaction of the tau_1 symmetry Sigma point mode with the planar O p_x and p_y states. The proposed interaction is found to naturally facilitate symmetry breaking associated with pairing and/or stripe formation. 
V.V.Kabanov and D.Mihailovic