SLOWNESS SURFACES, RAY VELOCITY SURFACES AND PHONON FOCUSING IN HIGH T-C SUPERCONDUCTOR CRYSTALS

This paper reports the results of the study of anisotropy in elastic w ave propagation in single crystal superconducting BSCCO. The inverse a nd group velocities of elastic waves propagating in different directio ns have been computed and the corresponding slowness and ray velocity surfaces plotted, taking elastic constant data from literature. In add ition, the phenomenon of phonon focussing has been investigated in thi s material by computing the phonon enhancement factor along different directions in spherical polar coordinates. The abnormally high values in phonon enhancement factor exhibited in certain directions for the p honon modes are interpreted as due to caustics occurring in the geomet rical acoustics approximation adopted in the computational analysis. T he results in LSCO and YBCO are found to be similar to those in BSCCO.