Optimization of shape and placement of superconducting junctions of SQUID by 2 dimensional scanning of external magnetic field

我们发现三角形结的约瑟夫森电流随外磁场的变化具有六角对称性。铌/铝氧化物/铌结的制作采用磁控溅射铌和铝层的热氧化。选择性铌阳极氧化工艺已被用来定义结区。在正方形结的情况下，由平行于氧化铝层的外场二维扫描得到的约瑟夫森电流的依赖关系，已成为平行于该正方形结区各边的H_x，H_y方向上的两个夫琅和费图形的乘积。在I_c-H（H_x，H_y）关系的（H_x，H_y）面中心，在主峰周围0、90、180和270度四个方向上观察到了次峰。我们还制作了三角形结，得到了约瑟夫森电流随磁场的变化曲线，在0、60、120、180、240和300 °六个方向上观察到次峰 ...更多信息 在（H_x，H_y）磁平面中心附近的0 °。这种磁性依赖性具有六方对称性。我们还模拟了假设在结区的均匀电流流动的依赖性。两个超导电极之间的规范不变相位差被调制垂直于势垒区域内的外部磁场方向，其中调制波长与所施加的磁场的大小成反比。模拟结果与实测数据吻合良好，并将结垂直叠加，得到了两个结势垒相互影响的双势垒结。两个屏障的这种干扰的强度可以通过两个屏障的分离来改变。这种分离很容易通过两个屏障之间的中间层的厚度来控制。通过快门控制，我们同时制作了多个具有不同中间层厚度的双势垒结。研究了双势垒结的差距电压和约瑟夫森超导电流与中间层厚度的关系。我们还研究了这种超导电流的二维磁场依赖性，并评估了这种干涉结构中外部磁场的有效捕获面积。少

We have found hexagonal symmetry in the dependence of Josephson current of triangle shape junctions upon external magnetic field. Niobium/aluminum-oxide/niobium junctions are fabricated using magnetron sputtering of niobium and thermal oxidation of aluminum layers. Selective niobium anodization process has been used to define junction areas. In the case of square shaped junction, dependence of Josephson current obtained by two dimensional scanning of the external field parallel to aluminium-oxide layer, have become the product of the two Fraunhofer patterns in the direction H_x, H_y parallel to each edge of this square junction area. Sub peaks have been observed in four directions at 0,90,180 and 270 degree around the main peak in the centre of the (H_x,H_y) plane of the I_c-H(H_x,Hy) dependence. We have also fabricated triangle shaped junctions and obtained the magnetic field dependence of Josephson current, where sub peaks can be observed in six directions at 0,60,120,180 240 and 300 … More degree around the centre of the (H_x,H_y) magnetic plane. This magnetic dependence has hexagonal symmetry. We also simulated the dependence assuming the uniform current flow in the junction area. The gauge-invariant-phase-difference between the two superconducting electrodes is modulated perpendicular to the external magnetic field direction inside the barrier region, where the modulation wavelength is inverse proportional to the magnitude of the applied magnetic field. Quite excellent agreement between the measured data and the simulation result has successfully been obtained.We have also stack the junctions vertically and obtained the double barrier junctions, where the two junction barriers would affect each other. The strength of this interference of the two barriers can be changed by the separation of the two barriers. This separation was easily controlled by the thickness of the middle layer between the two barriers. By the shutter control, we have made lots of double barrier junctions having different thickness of middle layers simultaneously. Dependence of the gap voltage and Josephson superconducting current through the double barrier junctions upon the thickness of the middle layer have been studied. We have also study the two dimensional magnetic field dependence of this superconducting current and have evaluated the effective capturing area of the external magnetic field in this interfering structure. Less