Anomalies of attenuation and phase velocity of surface acoustic waves in YBa₂Cu₃O_7‒δ thin films in the vicinity of T_c

Abstract:

We present measurements of the attenuation and phase velocity of surface acoustic waves in thin YBa₂Cu₃O YBa₂Cu₃O_7‒δ films as a function of temperature, in magnetic fields up to 3.6 T applied parallel to the c-axis of the films. We have observed anomalies in both, the attenuation and the phase velocity in the vicinity of the superconducting critical temperature which do not depend on the magnetic field. Possible origins of these anomalies, observed, to our knowledge, for the first time in YBa₂Cu₃O_7‒δ thin films, are discussed and compared to bulk acoustic wave experiments. We present a kind of feedback technique for surface acoustic waves which improves the sensitivity of this type of measurement. The actual sensitivity limits are mentioned.