Anelastic Relaxation in the High TC Superconductor YBa2Cu3O7-x

The first measurement of anelastic relaxation in a vibrating sample of YBa2Cu3O7-x is reported. A marked drop in the dissipation is observed below Tc, from which a strong electron-phonon interaction is inferred. It is found that the Bardeen-Cooper-Schrieffer theory with a gap of ?/KB=240 K can explain this drop. The data also suggest the occurrence of a phase transition at 235 K.