Surface acoustic wave investigation of mixed-state phases in YBa/sub 2/Cu/sub 3/O/sub 7/

A technique was developed which allows for surface acoustic wave (SAW) experiments up to 500 MHz in YBCO single crystals and films on piezoelectric as well as non-piezoelectric substrates. Experimental data on a granular YBCO film show a field dependent attenuation peak below T/sub c/ which is indicative of temperature dependent changes of the coupling of the magnetic vortex system to the crystal lattice and might be related to melting or depinning of the vortex lattice.