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New Ultrasonic Method to Investigate Flux Pinning Properties of Superconducting Thin Films

A new ultrasonic method has been proposed for the investigation of flux pinning properties of superconducting thin films. In the method, pinned flux lines are excited by the ultrasonic vibration of pinning centers, and depinned flux lines are detected in terms of the flow voltage generated by the Lorentz force due to transport current. By applying a parallel magnetic field and propagating AM ultrasound perpendicularly to the surface of YBa2Cu3O7-δ films, a maximum of AC voltage was observed below the onset temperature of the superconducting transition. From its dependence on the ultrasonic amplitude and the transport current, the observed voltage is found to be induced by flux flow normal to the surface raised by ultrasound.