Low field ultrasonic attenuation by the vortex lattice of melt-textured YBa/sub 2/Cu/sub 3/O/sub 7/

Measurements of the transverse ultrasonic attenuation and velocity on a melt-textured sample of YBa/sub 2/Cu/sub 3/O/sub 7/ (T/sub c/=87 K) were carried out in low magnetic field sweeps at fixed temperatures. Two frequencies (76.4 MHz and 10.6 MHz) were used in transverse sound attenuation measurements. A penetration field is determined by the midpoint of the rapid increase of either the attenuation or the relative velocity. Because of the lack of anisotropy of the penetration field with magnetic field orientation, the authors have previously identified it as the penetration field of the matrix surrounding the individual oriented crystallites. The attenuation jump appears to follow the penetration field above 60 K and drops exponentially below 50 K. A model is presented wherein both of these effects may be explained by an activation process or an energy gap which is associated with the dissipation part of the interaction.<>