Angular Dependence of Ultrasonic Attenuation at Hcl in YBa2Cu3O7 Single Crystal

The resistive behavior of type-II superconductors in the superconducting state is largely influenced by the materials' ability to pin magnetic flux lines. While an externally applied magnetic field leads to an ordered flux-lattice in defect-free superconductors, spatial variations in the superconducting order parameter tend to deform the vortex system. This has immediate implications for the temperatureand field-dependence of the critical current density. Simple estimates of the balance between the intervortex interaction and the vortexpinsite interaction dow for qualitative predictions of the temperature- and field-dependent resistive behavior of type-II superconductors. A low fiequency ultrasonic technique was developed, which was used to study the viscous properties of the vortex system