Research on novel vortex states in mesoscopic superconductors

对于具有与超导相干长度和/或磁穿透深度相当的尺寸的超导体，长期以来，理论上预测对磁场的响应与大块超导体的响应显著不同，导致形成诸如巨涡旋态（GVS）和多涡旋态（MVS）的新颖涡旋态：在超导体中，涡旋形成Abrikosov三角形点阵，而在介观薄膜中，涡旋的排列反映了样品的形状，或者多个涡旋联合收割机合成一个，形成巨涡旋。在2004年，我们通过实验验证了这些涡旋态的存在，第一次使用我们的原始技术，多小隧道结（MSTJ）方法。从2005年开始的本研究中，我们获得了以下结果：（1）我们找到了一种利用涡驱逐场的温度依赖性来区分GVS和MVSS的通用方法;（2）我们实验证实了GVS和MVSS的相互关系，并在实验上验证了GVS和MVSS的相互关系。 ...更多信息 （3）验证了一维涡旋在介观环中的存在性，这一预言已被提出20多年，但从未得到证实，发现了一种新的超导涨落效应，它依赖于环中的外加磁通量。（5）寻找了理论上预言的反涡旋，（6）发展了一种确定含2 × 2纳米孔超导体中涡旋位置的方法;（7）发展了一种通过外部参数控制涡旋态的方法。通过与秋田大学和安特卫普大学的理论小组的密切合作，我们弄清了这些现象的背景物理。我们的成功结果不仅使我们更好地理解了小区域量子系统的物理特性，而且为未来基于纳米超导工程的器件应用开辟了道路。少

For superconductors with sizes comparable to the superconducting coherence length and/or the magnetic penetration depth, it has been theoretically predicted for a long time that the response to magnetic field is significantly different from that of bulk superconductors, leading to formation of novel vortex states such as giant vortex states (GVSs) and multivortex states (MVSs): While in bulk superconductors vortices form Abrikosov triangular lattice, in mesoscopic thin films, vortex arrangement reflects the sample shape, or multiples vortices combine into one, forming a giant vortex. In 2004, we experimentally verified the existence of these vortex states for the first time by using our original technique, multiple-small-tunnel-junction (MSTJ) method. In the present research started in 2005, we have obtained the following results: (1) We found a general method for distinction between GVSs and MVSs using the temperature dependence of vortex expulsion fields, (2) We experimentally confir … More med the basic properties of novel vortex states such as sample-shape and temperature dependence of vortex states, relationship between stability of vortices and sample geometry and effect of defects, (3) We verified the existence of one-dimensional (1D) vortex in mesoscopic rings, which has been predicted for more than 20 years but never confirmed, and showed that the nonuniform cross section is crucial for the stabilization of the 1D vortex, (4) We found a new effect of superconducting fluctuation which depends on the applied flux in rings, (5) We searched for the theoretically-predicted antivortices, and determined the parameter range for the existence of antivortices, (6) We developed a method to determine the position of vortices in a superconductor with 2x2 nanoholes, and (7) We developed a method to control the vortex states by external parameters. We made clear the background physics of these phenomena by the close collaboration with theoretical groups of Akita Univ. and Univ. Antwerp. Our successful results not only give a better understanding of the physics of quantum systems confined in small area, but also open the way for the future device application based on nanoscale superconductivity engineering. Less