Phonon Softening and Electron-Phonon Interaction in YBa2Cu3O7−δ

We report on the Raman scattering investigation of the 335 cm−1 phonon of Ag (pseudo-B1g) symmetry in thin YBa2Cu3O7−δfilms on various substrates. The experiments yield values for the phonon softening below Tc, which differ from sample to sample. We find a linear relation between the softening and the inverse asymmetry parameter of the phonon Fano-like lineshape, when these parameters, obtained from different samples, are compared with each other. In contrast to this, the onset temperatures for the softening are the same for these samples.