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，而另一些材料绝缘体则完全不带电。然而，许多在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的过渡边缘的系统进行实验，在这种边缘应该发生混合行为。在一个案例中，他们正在使用纳米技术驱动超导体成为绝缘体，方法是将超导体制成比纳米(十亿分之一米)更薄的薄膜，并在上面穿孔成纳米级的孔。在第二种情况下，他们正在创造超导体和金属的双层薄膜，在这些金属和超导相之间产生直接竞争。这些研究是布朗大学两名研究生的博士研究培训。这些学生将发展纳米技术、高灵敏度电学测量和低温技术方面的专业知识，这些技术将使他们对工业具有吸引力。此外，物理专业的本科生将参与这项研究，作为高级论文项目的一部分。TechnicalValles的团队正在研究超薄超导薄膜，通过降低它们的超导序参数幅度，使其处于向非超导相转变的边缘。这项工作的重点是超导体的两个不同的微观特征：磁涡旋和超导准粒子。超导相和非超导相之间的共存和竞争取决于涡旋运动和准粒子分布。这一结果可能会让人们对高温超导体和其他技术前景看好的材料中发生的类似阶段竞争有更深入的了解。其中一组超低温研究使用了超薄的均匀超导薄膜，该薄膜具有纳米尺寸的六角形阵列和间隔的孔。这些可以钉住涡旋的孔洞将被用来检测涡旋运动对二维超导体向绝缘体转变的影响。第二项工作使用电子隧穿来表征超薄超导体-正常金属双层中出现的准粒子态密度的异常。在这些复合薄膜中，这些态可以驱动超导体到金属的量子相变。这些调查作为布朗大学两名研究生的博士研究培训。这些学生将发展纳米技术、高灵敏度电气测量和低温技术方面的专业知识，这些技术将使他们对工业具有吸引力。此外，物理专业本科生将从事相关的高级论文项目。

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.