Interaction between novel vortices in nano-structured superconductors

本文提出了一种用双分量Ginzburug-Landau方程模拟d点系统的方法。使用这个模拟，它表明，两个d点之间的相互作用成为一个新的，它取决于它们之间的距离和方向。特别是，两个半量子通量的融合发生在短距离内，并影响相互作用。利用这种相互作用，提出了新的超导逻辑门。数值模拟结果证实了它们的有效性。研究表明，它们的运算速度可达皮秒量级，d-dot逻辑电路将成为下一代计算机的理想候选电路。基于Bogoliubov-de Gennes方程，发展了一种研究任意形状纳米超导体微观特性的模拟方法。利用这种方法，两个涡之间的相互作用进行了研究。并且发现了涡旋分子态 关于我们 显示出类似分子轨道的状态。这种性质影响了相互作用，从唯象理论来看，这种相互作用被认为是纯粹排斥的。这种相互作用影响了涡的结构，其中涡的距离相当短。此外，我们还发现纳米超导体所特有的巨涡旋周围的准粒子结构不同于单量子化涡旋。利用类似的方法，我们证明了纳米尺度的各向异性超导体。由于各向异性超导体的节态被限制在能隙中，因此在能隙一侧具有调制的准粒子态。这些性质可以通过扫描隧道谱实验得到证实。本文提出了一种用一维和二维有限元相结合的方法模拟超导网络中涡旋动力学的方法。利用这种模拟方法，我们发现非对称有限超导网络表现出棘轮效应，即在外加交流电作用下网络中的涡旋运动。电流引起直流电压，并研究了多孔超导体模型随机超导网络的涡旋结构。由于涡旋的随机性导致的反常涡旋钉扎，使相变温度降低，涡旋呈现出特殊的结构。这一结果表明，这种多孔超导体是高Jc超导材料的良好候选者。少

A simulation method for d-dot systems, which are composite structures of d- and s-wave superconductors, are developed, using two-components Ginzburug-Landau equations. Using this simulation, it is shown that interaction between two d-dot's becomes novel one and it depends on the distance and directions between them. Especially, fusion of two half-quantum fluxes occurs in short distance and it affects the interaction. Using this interaction, novel superconducting logic gates are proposed. And their operation is confirmed by the numerical simulations. Also it is shown that their operation speed is order of pico-second and d-dot logic circuit become good candidate for a computer of the next generation.A simulation method for investigation of microscopic properties of arbitrary shaped nano-sized superconductors is developed using the Bogoliubov-de Gennes equations. Using this method, interaction between two vortices is investigated. And a vortex molecule state is found. The quasi-particles … More around it show molecular orbital-like states. This property affect the interaction, which was believe to be purely repulsive from the phenomenological theory. This interaction affects the vortex configuration, in which the distance of vortices is rather short. Also quasi-particle structure around a giant vortex, which is peculiar to the nano-sized superconductors, is found to be different from that of a singly quantized vortex. Using similar method, it is shown that nano-sized anisotropic superconductors. have the modulated quasi-particle states in side of the energy gap, because of the confinement of the nodal states in the energy gap of anisotropic superconductors. These properties can be confirmed by the scanning tunneling spectroscopy experiment.Simulation method for dynamics of vortices in the superconducting networks is developed, by using combined one-dimensional and two-dimensional finite element method. Using this simulation method, it is shown that asymmetric finite superconducting networks shows ratchet effect, i.e. the vortex motion in these networks under external A.C. current causes D.C. voltage.Also vortex structure of random superconducting networks, which are models of porous superconductors, is investigated. Because of anomalous vortex pinning, which comes from their randomness, the transition temperature becomes low and vortices show peculiar structure. This result shows that such porous superconductors are good candidate for high Jc superconducting materials. Less