Quantum Phase Transitions in Nanostructured Superconductors in 2D

该个人研究者奖将支持一个实验项目，该项目关注准二维（2D），纳米结构薄膜在超导体到非超导体量子相变（QPTs）附近。由嵌在金属薄膜中的纳米级超导颗粒和超导薄膜的纳米级线阵列组成的纳米结构邻近效应阵列将通过其超导体转变为非超导体，并在稀释冰箱温度下通过电子磁输运和隧道测量进行探测。纳米阵列中量子点背后的物理原理，虽然类似于众所周知的超导体到绝缘体的转变，但预计将与它们形成鲜明对比。由于纳米尺度的尺寸，在这些转变过程中，超导序参量中的相位和振幅自由度，而不仅仅是相位，将会发生强烈的变化。这些实验有可能揭示新的qpt类别，并为二维相关电子系统（如欠掺杂高温超导体）中的赝隙和非常规金属相的起源提供物理见解。在沉浸于凝聚态物理的重要当前问题的同时，参与这项研究的学生将发展纳米技术，扫描探针显微镜和低温技术方面的专业知识，这些技术将使他们对工业界具有潜在的吸引力，并为他们成为未来的科学领导者做好准备。生产和获取电子材料图像的能力，其特征小至几十亿分之一米（几纳米），为技术和基础科学带来了新的机遇。在技术上，随着我们对计算机的速度和功率的要求越来越高，电子产品的尺寸必然迅速缩小到纳米级。从根本上说，当金属铜的尺寸缩小到纳米尺度时，它可能会出现新的特性。一块铜能有多小，还能保持通常与金属有关的特性？这个个人研究者奖支持一个项目，该项目关注的是超导材料（即当冷却到接近绝对零度时失去所有电阻的材料）的特性在某些尺寸缩小到几纳米尺度时是如何变化的。对两种结构的测量，纳米结构接近效应阵列和纳米级超导线阵列，将检验最近的理论，这些理论认为，当超导体的尺寸变得足够小时，它们会经历一个巨大的变化，变得更像金属状态的物质。据预测，这种金属状态具有与技术相关的高温超导体材料相似的奇异特性。因此，这些纳米结构的超导体将作为一个模型系统，可以为其他更复杂的材料提供新的见解。此外，它们将被用来解决一个简单而基本的问题，即超导体的结构如何精细，同时仍能保持其超导特性？在沉浸于凝聚态物理的重要当前问题的同时，参与这项研究的学生将发展纳米技术，扫描探针显微镜和低温技术方面的专业知识，这些技术将使他们对工业界具有潜在的吸引力，并为他们成为未来的科学领导者做好准备。

This individual investigator award will support an experimental project that focuses on quasi-two-dimensional (2D), nanostructured films near their superconductor to nonsuperconductor quantum phase transitions (QPTs). Nanostructured proximity effect arrays, consisting of nanoscale superconducting grains embedded in a metal film and nanoscale wire arrays of superconducting films will be tuned through their superconductor to non-superconductor transitions and probed with electron magnetotransport and tunneling measurements at dilution refrigerator temperatures. The physics behind the QPTs in the nano-arrays, while similar to the well-known superconductor to insulator transitions is expected to sharply contrast with them. Because of the nanoscale dimensions, the phase and amplitude degrees of freedom in the superconducting order parameter, rather than just the phase, will vary strongly through these transitions. These experiments have the potential to reveal new classes of QPTs, and to provide physical insight into the origin of pseudogaps, and unconventional metallic phases in 2D correlated electron systems, such as the underdoped high temperature superconductors. While being immersed in important current problems in condensed matter physics, the students involved in this research will develop expertise in nanotechnology, scanning probe microscopies and low temperature techniques that will make them potentially attractive to industry and prepare them to be future leaders in science.The ability to produce and obtain images of electronic materials with features as small as a few billionths of a meter (a few nanometers) leads to new opportunities in technology and fundamental science. In technology, as more speed and power is demanded from our computers the dimensions of the electronics necessarily rapidly shrink toward the nanodimensions. On a fundamental side, new properties can emerge in seemingly familiar materials such as the metal copper when its dimensions are reduced to the nanometer scale. How small can a piece of copper be and still maintain the properties which are commonly associated with a metal? This individual investigator award supports a project that focuses on how the properties of superconducting materials (i.e. materials which lose all of their electrical resistance when cooled close to the absolute zero of temperature) change when some of their dimensions are pared down to the few nanometer scale. Measurements on two types of structures, nanostructured proximity effect arrays and nanoscale superconducting wire arrays, will test recent theories that suggest that the superconductors go through a dramatic change, becoming more like a metallic state of matter, when their dimensions become small enough. This metal state is predicted to have exotic properties that are similar to those of the technologically relevant high temperature superconductor materials. Thus, these nanostructured superconductors will serve as a model system that can lend new insight into other more complex materials. In addition, they will be used to address the simple and fundamental question of how finely structured can a superconductor be and still maintain its superconducting properties? While being immersed in important current problems in condensed matter physics, the students involved in this research will develop expertise in nanotechnology, scanning probe microscopies and low temperature techniques that will make them potentially attractive to industry and prepare them to be future leaders in science.