Exploring Quantum Effects in Two-Dimensional Multilayered Superconductors

* 技术摘要 * 二维超导体相图的研究与寻找新材料密切相关。对于每个材质系统，将亮显一组不同的属性。多年来，NSF的支持使得各种材料的优化成为可能，用于研究一般的超导薄膜，特别是超导体到绝缘体的转变（SIT）。这些包括允许发现“金属相”的非晶MoGe膜，允许研究强无序状态的非晶InOx膜，允许详细研究过渡附近的霍尔效应的非晶TaNx，以及非晶MgB 2膜，除了与MoGe，TaNx和InOx的参数重叠之外，还提供了一种新的控制自旋轨道相互作用的旋钮。这个项目探讨了超导体-绝缘体转变附近的丰富相图，重点是介入的金属态。特别是，我们将集中在理解什么是真正的二维SIT在金属背景（即耗散）的存在下的相图;什么是二维SIT系统的电子微观结构;我们可以推断出各种长度尺度的实验，如运输，霍尔和能斯特效应等;并且，从金属膜上有序金属点制成的人造膜开始，随着我们增加无序度，这种方法的有效性范围是什么。这项拟议中的工作预计将为减少维度的量子相变的性质提供新的见解，并影响对非晶超导薄膜材料科学的理解。非技术摘要 * 量子相变继续吸引着强烈的理论和实验兴趣。这种转变-改变哈密顿量中的外部参数会导致从一个量子基态到另一个量子基态的转变，从根本上讲是不同的-已经被用来理解许多电子系统中的实验数据，以及分析更具挑战性的量子现象，例如量子计算的局限性。量子相变的一个范例是二维薄膜中的超导体到绝缘体的转变。这种转变被发现有各种实现取决于所使用的材料的固有特性。控制薄膜的超导性、无序性或维度的强度将影响转变的性质，这是通过改变外部参数如温度和磁场来实现的。该奖项支持一个项目，以探索一系列独特的量子状态附近的超导体到绝缘体过渡的非晶薄膜，特别是非晶钼锗，硼化镁，铟和氮化钽。这组系统的独特之处在于能够在非常广泛的参数范围内控制超导性和无序的强度，特别是允许访问我们小组首次发现的知之甚少的无处不在的金属态。该计划涉及对物理学和未来应用非常感兴趣的这一领域的研究生。

****Technical Abstract****Studies of the phase diagram of two-dimensional superconductors has been intimately connected to finding new materials. With each materials system a different set of properties is highlighted. Over the years, NSF support enabled the optimization of a variety of materials for studies of thin superconducting films in general and the superconductor to insulator transition (SIT) in particular. These include amorphous-MoGe films that allowed the discovery of "metallic phases," amorphous-InOx films that allowed the studies of the regime of strong disorder, amorphous TaNx that allowed for the detailed study of the Hall effect near the transition, and amorphous- MgB2 films which in addition to the overlap in parameters with MoGe, TaNx, and InOx, also provide a new knob in the form of controlling spin-orbit interaction. This project explores the rich phase diagram near the superconductor-insulator transition with emphasis on the intervening metallic states. In particular we will concentrate on understanding of what is the true phase diagram of two-dimensional SIT in the presence of a metallic background (i.e. dissipation); what is the electronic microstructure of a 2D SIT system; can we infer the various length scales from experiments such as transport, Hall and Nernst effects, etc.; and, starting from artificial films made of orderly metallic dots on a metal films, what is the range of validity of this approach as we increase disorder. The proposed work is expected to shed new light on the nature of quantum phase transitions in reduced dimensions and impact the understanding of the material science of amorphous superconducting films.****Non-Technical Abstract****Quantum phase transitions continue to attract intense theoretical and experimental interest. Such transitions -- where changing an external parameter in the Hamiltonian induces a transition from one quantum ground state to another, fundamentally different one -- have been invoked to understand experimental data in many electronic systems, as well as to analyze more challenging quantum phenomena such as the limitations of quantum computing. A paradigm for quantum phase transitions has been the superconductor to insulator transition in two-dimensional films. This transition is found to have a variety of realizations depending on intrinsic properties of the materials used. Controlling the strength of superconductivity, disorder, or dimensionality of the films will impact the nature of the transition, which is accessed through the variation of external parameters such as temperature and magnetic field. This award supports a project to explore a series of unique quantum states near the superconductor to insulator transition in amorphous films, particularly amorphous-MoGe, MgB2, InOx and TaNx. The uniqueness of this set of systems is the ability to control the strength of superconductivity and disorder over a very wide range of parameters, and and in particular allow access to the poorly understood ubiquitous metallic states that have been first identified by our group. The program involves graduate students in this area of great interest to physics and future applications.