Acoustic Studies of Single Crystal High Temperature Superconductors

The acoustic properties of single crystals of the high temperature superconductor YBa sub 2 Cu sub 3 O sub 7 have been measured at temperatures between 0.1 and 300K for frequencies near 10 sup 3 and 10 sup 9 Hz. In the GHz regime, longitudinal modes have been studied for propagation directions parallel and perpendicular to the c-axis. At T sub c, there is a discontinuity in the sound velocities and their temperature derivatives from which the anisotropic strain dependences of T sub c are obtained. In the kHz regime, resonant excitation of flexural modes in thin reeds of YBa sub 2 Cu sub 3 O sub 7 crystals has permitted precise measurement of acoustic damping and dispersion.