Magneto-optical study on control and dynamics of magnetic flux quanta

1.我们研制了一套自制的磁光显微镜系统，成功地观测了高温超导体BSCCO（2212）单晶中磁通量的量子分布.我们在液相外延法生长的单晶中成功地观察到了磁通量子的Abrikosov晶格结构。另一方面，在TSFZ法生长的单晶中，可重复地观察到a轴取向的磁通量子分布，这可能是由于晶体生长过程中引入了一些非本征缺陷.我们用金属有机分解法制备了Bi、Ga取代的铁石榴石，并对其作为MO指示剂的性能进行了优化。发现厚度约为1.4 μ m的石榴石膜可获得最高灵敏度的指示剂.我们研制了空间分辨率小于0.5 μm的激光扫描MO成像系统。为了检验其性能，我们利用YBCO超导磁通流型装置进行了一系列实验，并成功地动态观测了偏置电流作用下控制线周围产生的磁场。在准静态磁场条件下，系统的磁灵敏度可达几μT（特斯拉），在动态观测模式下，系统的磁灵敏度可达几十μT。实验结果表明，该系统具有足够的灵敏度，可以动态检测超导器件中的磁通量量子.我们制作了一种具有平行约瑟夫森结阵列的约瑟夫森涡流晶体管，并通过在控制电流线上施加直流电流或将调制的飞秒光脉冲照射到约瑟夫森结上，成功地观察到了临界电流和流动电压的明显调制。

1. We have developed a homemade magneto-optical (MO) microscope system and succeeded in the observation of the magnetic flux quantum distribution in high-Tc superconductor BSCCO(2212) single crystals.2. We have succeeded in the observation of the Abrikosov lattice-like structures of magnetic flux quanta in the single crystals grown by LPE method. On the other hand, a-axis aligned distribution of magnetic flux quanta was reproducibly observed in the single crystals grown by TSFZ method, probably due to some extrinsic defects introduced in the crystal growth.3. We have prepared Bi, Ga substituted iron garnet by the metal organic decomposition method, and optimized its characteristics as a MO indicator. It was found out that the highest sensitive indicator can be obtained for the garnet film with the thickness of about 1.4 μm.4. We have developed a laser scanning MO imaging system which has a spatial resolution less 0.5 μm. In order to check the performance, we have carried out a series of experiments by using superconducting flux flow type devices of YBCO, and succeeded in the dynamic observation of the magnetic field generated around the control line applied with bias current. It was also confirmed that the magnetic sensitivity of the system is as good as several μT (tesla) in a quasi static magnetic field condition, and several 10 μT in a dynamic observation mode. This result shows that the developed system has an enough sensitivity to dynamically detect the magnetic flux quantum in superconducting devices.5. We fabricated Josephson vortex flow transistors with a parallel array of Josephson junctions, and succeeded in the observation of clear modulations of critical current and the flow voltage by applying DC current to the control current line or by illuminating modulated femtosecond optical pulse to the Josephson junctions.