Superconductors, Insulators, Metals and Quantum Phase Transitions in Two-Dimensional Films

虽然“经典”相变已经成功解释了很多年，但有限温度，无序和耗散的影响是将相同的方法应用于量子相变（QPT）时要谨慎的几个原因，特别是低维材料中的QPT。二维QPT的一个重要原型系统是薄膜中的超导体-绝缘体转变（SIT），其中所有上述效应都起着重要作用。 该项目将通过使用非晶InOx薄膜来扩展SIT的早期工作，精心制作以避免颗粒效应，以探索与耗散和无序效应相关的问题。在这种材料中，振幅波动变得重要，从而影响整体SIT行为。要研究的重要影响包括在耗散的存在下SIT的相图;过渡附近的SIT系统的电子微观结构和电子相分离的搜索;耗散的可能来源;低场超导体-金属过渡;和绝缘相的性质，以及其初期的超导行为。 除了该项目的重要知识内容，涉及凝聚态物理学的许多领域，包括对高温超导体的理解，它还将作为PI教授的新研究生课程的基础，通过拟议项目的概念和结果向学生介绍QPT。 参加本研究项目的学生将学习技能，为他们未来在学术界、工业界或国家实验室的职业生涯做好准备。未来的计算机和其他电子系统的核心设备越来越多地依赖于量子力学。 例如，将构建未来量子计算机的量子位依赖于改变系统中的外部参数的能力，该参数诱导从一个量子基态到另一个量子基态的跃迁。 当这个量子比特由宏观系统（例如磁矩的宏观样本）表示时，从一个量子态到另一个量子态的跃迁表示量子相变（QPT）。 理解QPT对于一般的凝聚态系统也非常重要，因为它几乎出现在低温下的每个量子系统中。 耗散和无序效应将成为器件的限制性效应，同时也对QPT的理论理解提出了挑战。 薄膜中的超导体-绝缘体转变（SIT）是存在这些限制效应的QPT模型系统。 制造具有良好控制其电子性质和无序的薄膜的能力提供了一个独特的机会来回答QPT和未来量子器件物理学上的许多开放问题。 从事该项目的研究生将学习技能，为他们未来的科学或技术职业做好准备。 科学和大众出版物以及PI将教授的关于该主题的新课程将成为传播该项目成果的主要场所。

While "classical" phase transitions have been explained successfully for many years, the effects of finite temperature, disorder, and dissipation are several reasons to exercise caution when applying the same approach to quantum phase transitions (QPT), and in particular QPT in low-dimensional materials. An important prototype system for 2-dimensional QPT is the superconductor-insulator transition (SIT) in thin films where all the above effects play an important role. This project will extend earlier work on the SIT by using amorphous InOx films, carefully fabricated to avoid granular effects to explore issues related to dissipation and disorder effects. In such materials amplitude fluctuations become important and thus affect the overall SIT behavior. Important effects to be studied include the phase diagram of the SIT in the presence of dissipation; the electronic microstructure of SIT system near the transition and the search for electronic phase separation; the possible sources of dissipation; the low-field superconductor-metal transition; and the nature of the insulating phase, and its incipient superconducting behavior. Besides the important intellectual content of the project that bears on many areas of condensed matter physics, including the understanding of high-Tc superconductors, it will also serve as a basis for a new graduate level course that will be taught by the PI, introducing QPT to the students through concepts and results of the proposed project. The students participating in this research project will learn skills that will equip them for future careers in academia, industry, or national laboratories.%%%Future devices that will be in the heart of computers and other electronic systems are increasingly expected to depend on quantum mechanics. For example a qubit that will build a future quantum computer relies on the ability to change an external parameter in the system that induces a transition from one quantum ground state to another. When this qubit is represented by a macroscopic system (e.g. a macroscopic sample of magnetic moments), a transition from one quantum state to another represents a quantum phase transition (QPT). Understanding QPT is also of chief importance for general condensed matter systems as it appears in almost every quantum system at low temperatures. Effects of dissipation and disorder are expected to be limiting effects for devices and at the same time pose challenge for theoretical understanding of QPT. The superconductor-insulator transition (SIT) in thin-films is a model system for QPT in the presence of those limiting effects. The ability to fabricate films with good control of their electronic properties and disorder provides a unique opportunity to answer many of the open questions that bear on the physics of QPT and future quantum devices. Graduate students working on the project will learn skills that will equip them for future scientific or technological careers. Scientific and popular publications, as well as a new course that will be taught by the PI on the subject will be the main venue to communicate the results of this project.