Ultrasonic Excitation of Magnetic Flux Flow in Multilayered Thin Films of Superconductor-Piezoelectric Material

这个项目是一个两年的计划。然而，由于激光烧蚀设备的制造比原计划推迟，多层薄膜的制备没有成功。在制备的同时，采用直流溅射法制备了BiSrCaCuO薄膜，并测量了超声激发下的磁通流电压。实验结果对超导体压电材料薄膜的测量具有一定的指导意义。为了获得高质量的薄膜，研究了缓冲层对BiSrCaCuO层结晶度和超导性的影响。发现缓冲层可以降低薄膜与衬底之间晶格不匹配引起的应变，提高超导转变温度和薄膜表面的粗糙度。对上述薄膜和烧结体试样进行了纵向超声激发的磁通流电压测量。基于热辅助通量流模型的实验结果与理论结果进行了比较，指出了有待解决的问题。用不同的超声振动模式测量了磁通流电压，这与磁通线晶格的熔化有关。观察到磁通流动电压的特征现象。

This project was schemed as a two-year plan. However, the preparation of multilayered thin films was not succeeded, because the fabrication of the equipment of the laser ablation was delayed from the initial plan. In parallel to the fabrication, BiSrCaCuO thin films were prepared using a dc sputtering, and the flux flow voltage excited by ultrasound was measured. The experimental results which will give some information for the measurements using thin films of superconductor-piezoelectric materials were obtained as follows :1. The effects of buffer layers on the crystallinity and superconductivity of BiSrCaCuO layer were studied to get high quality thin films. The buffer layers were found to reduce the strain caused by the lattice mismatch between the films and the substrates, and improve the superconducting transition temperature and the roughness of the film surface.2. The magnetic flux flow voltage excited by longitudinal ultrasound was measured for the above thin films and the bulk sintered samples. The experimental results were compared with theoretical ones based on the model of thermally assisted flux flow, and the problems to be solved were pointed out.3. The flux flow voltage was measured with a different vibrational mode of ultrasound which is related to the melting of the flux line lattice. A characteristic phenomenon was observed for the flux flow voltage.