Vorticles and Quasiparticles in Superconducting Films in the Small Order Parameter Amplitude Limit

非技术物理学家可以解释为什么有些材料表现为磁铁，有些材料表现为超导体，还有一些材料是绝缘体，根本不导电。然而，许多技术上很有前途的新材料表现出混合的性质，不适合这些传统的物质相。为了深入了解这种混合相行为的起源和表现，Valles的团队正在超低温下对处于超导和非超导相之间过渡边缘的系统进行实验，在那里混合行为应该发生。在一种情况下，他们利用纳米技术将超导体制成比纳米（十亿分之一米）还薄的薄膜，并在上面打上纳米级的孔，从而使超导体变成绝缘体。在第二种情况下，他们正在制造超导体和金属的双层薄膜，在金属和超导体之间产生直接竞争。这些研究是布朗大学两名研究生的博士研究训练。学生们将在纳米技术、高灵敏度电测量和低温技术方面发展专业知识，这将使他们对工业界具有吸引力。此外，物理专业的本科学生将参与本研究，作为毕业论文项目的一部分。TechnicalValles的团队正在研究超薄超导薄膜，通过减少超导序参量振幅，将超薄超导薄膜推向向非超导相变的边缘。这项工作的重点是超导体的两个不同的微观特征：磁涡流和超导准粒子。超导相和非超导相的共存和竞争取决于涡旋运动和准粒子分布。这一结果可能会为高温超导体和其他技术上有前途的材料中类似的相竞争提供见解。其中一组超低温研究采用超薄均匀超导薄膜，薄膜上有纳米尺度的六边形阵列和间隔孔。这些可以固定涡流的空穴将被用来检测涡流运动对二维超导体向绝缘体转变的影响。第二项努力是利用电子隧道来表征超薄超导体-正常金属双分子层中出现的准粒子态密度的异常。这些态可能在这些复合薄膜中驱动超导体向金属量子相变。这些调查是布朗大学两名研究生的博士研究训练。这些学生将发展纳米技术、高灵敏度电测量和低温技术方面的专业知识，这将使他们对工业界具有吸引力。此外，物理专业本科学生还将参与相关的毕业论文项目。

Non TechnicalPhysicists can explain why some materials behave as magnets, others as superconductors and others, insulators, do not carry electricity at all. Many technologically promising new materials, however, exhibit a mixture of properties and do not fit within these traditional phases of matter. To gain insight into the origins and manifestations of such mixed phase behavior, Valles' group is performing experiments at ultra-low temperatures on systems perched on the brink of a transition between a superconducting and a non-superconducting phase where mixed behavior should occur. In one case, they are using nano-technology to drive superconductors to become insulators by making them in the form of films thinner than a nano-meter (billionth of a meter) and perforated with nano-meter scale holes. In a second case, they are creating double layered films of a superconductor and a metal that produces a direct competition between these the metal and superconductor phases. These studies are serving as the PhD research training for two graduate students at Brown University. The students will develop expertise in nanotechnology, high sensitivity electrical measurements and low temperature techniques that will make them attractive to industry. In addition, undergraduate physics majors will engage in this research as part of senior thesis projects. TechnicalValles' group is investigating ultrathin superconducting films driven to the brink of a transition to a non-superconducting phase by the reduction of their superconducting order parameter amplitude. The work focuses on two distinguishing microscopic features of the superconductor: magnetic vortices and superconducting quasiparticles. The coexistence and competition between the superconducting and non-superconducting phases depend upon the vortex motion and the quasiparticle distribution. The results potentially will lend insight into similar phase competitions occurring in high temperature superconductors and other technologically promising materials. One set of these ultralow temperature investigations employs ultrathin homogeneous superconducting films patterned with hexagonal arrays of nanoscale size and spaced holes. The holes, which can pin vortices, will be used to detect the influence of vortex motion on the two dimensional superconductor to insulator transition. The second effort uses electron tunneling to characterize anomalies in the density of quasiparticle states that appear in ultrathin superconductor-normal metal bilayers. These states may drive a proposed superconductor to metal quantum phase transition in these composite films. The investigations serve as the PhD research training for two graduate students at Brown. These students will develop expertise in nanotechnology, high sensitivity electrical measurements and low temperature techniques that will make them attractive to industry. In addition, undergraduate physics majors will engage in related senior thesis projects.