Ultrasonic velocity in Zn substituted GdBaSrCu3O7−δ superconductor

Longitudinal and shear ultrasonic velocity in Zn substituted GdBaSr(Cu3−xZnx)O7−δ (x=0, 0.01, 0.03, 0.06 and 0.1) superconductors have been measured using the pulsed-echo-overlap method with frequency 5-10 MHz in the temperature range of 80-300 K. An elastic anomaly characterized by a slope change was observed in the x=0 sample in the longitudinal mode at around 220 K. This anomaly shifts towards lower temperature with increasing Zn content and vanishes when x=0.06 and 0.1. The characteristic Debye temperature and electron-phonon coupling constant were estimated using the standard BCS theory as well as the two-dimensional van Hove scenario. The variation in the elastic behaviours upon Zn doping may be due to the effect of changes in the spin correlation at the CuO2 planes.