Superconductor-(Metal)-Insulator Transitions: Understanding the Emergence of Metallic States, A Continuation Proposal

非技术摘要：最近越来越多的实验揭示了一种可能的“反常金属态”(AMS)，它表现出不能根据固体系统中电子的“标准范例”来理解的性质。该项目旨在探索异常金属相出现的程度及其与失效的超导和/或绝缘状态的关系。此外，该项目还探索了多种情况下AMS的可能变体。预计结果将揭示物质的一种新的金属状态，并将对物理学作为一门学科、对教育和社会产生影响。由于对自然界中的一种基本物质缺乏充分的了解，这应该会引发社会各阶层的好奇心，从而有助于提高我们的科学理解和可能产生的影响技术应用。技术摘要：最近越来越多的无序超导薄膜实验，最初是为了寻找超导体-绝缘体转变(SIT)，已经指出了从超导体到“反常金属状态”(AMS)零温度转变的可能性，这种转变具有“失效超导体”的特性。这种状态表现出显著的超导关联，然而即使在零温度下，系统也不能全局凝聚，通过量子超导体到金属的跃迁(QSMT)以有限的电导率沉淀。此外，在研究强烈不均匀系统的情况下，超导岛的充电能量通常通过库仑阻塞而导致绝缘状态，当电荷减弱时，可能会经历电荷波动，从而阻止真正的绝缘体的建立。随着对偏离“标准范式”的观察结果的快速累积，特别是在二维极限中，很明显，随着温度趋于零，存在着一类新的金属状态，其中的电子性质不能基于费米液体和德鲁德理论来远程理解，从而指向了自然界中金属状态的新范式。探索SIT和反常金属状态及其性质的出现是本项目的重点。这是通过专注于使用高颗粒膜或非传统超导体(如超导/铁磁双层)的增强型相波动材料，以及低温磁传输测量(包括对外部扰动的敏感性和用于研究超流体响应的改进的互感探头)来实现的。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Nontechnical Abstract: An increasing number of recent experiments reveal a possible “anomalous metallic state” (AMS), which exhibits properties that cannot be understood on the basis of “standard paradigms” of electrons in solid-state systems. The project aims to explore the extent of the emergence of the anomalous metallic phase and its relation to a failed superconducting and/or insulating states. Furthermore, the project explores possible variants of the AMS in multiple cases. Results are expected to shed light on a new class of metallic states of matter and will have an impact on physics as a discipline, on education and on society. Pointing to a lack of full understanding of one of the fundamental types of substances in nature, it ought to trigger curiosity at all levels of society, thus helping to enhance our scientific understanding and possible impact technological applications.Technical Abstract: An increasing number of recent experiments on disordered superconducting films, initially searching for a superconductor-insulator transition (SIT), have been pointing to the possibility of a zero-temperature transition from a superconductor to an “anomalous metallic state” (AMS) that features properties of a “failed superconductor.” This state exhibits significant superconducting correlations, yet the system fails to globally condense even at zero temperature, settling at a finite conductivity through a quantum superconductor to metal transition (QSMT). Furthermore, where strongly inhomogeneous systems are studied, charging energy of the superconducting islands, which typically leads to an insulating state through Coulomb blockade, can experience charge fluctuations when weakened, preventing the establishment of a true insulator. As observation of deviations from the “standard paradigm,” particularly in the limit of two-dimensions, have been fast accumulating, it becomes clear that there exists a new class of metallic states as the temperature tends to zero, where the electronic properties cannot remotely be understood on the basis of Fermi liquid and Drude theories, thus pointing to a new paradigm for metallic states in nature. Exploring SIT and the emergence of anomalous metallic states and their properties are the focus of this projects. This is achieved through focus on enhanced phase fluctuations materials either using highly granular films or unconventional superconductors such as superconductor/ferromagnet bilayers, as well as low-temperature magneto-transport measurements including sensitivity to external perturbations and improved mutual-inductance probe for the study of superfluid response.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.