Tunneling and Transport in Ordered and Disordered Superconductors

超薄金属薄膜和有机晶场效应晶体管结构中的超导体-绝缘体(SI)相变可以由外部控制参数来调节，并且被认为是由量子涨落而不是热涨落驱动的零温度量子相变。SI相变的基本物理模型的性质是不确定的，因为现有的实验没有区分竞争的费米子和玻色子描述，而且可能有一个明显的金属相分隔超导和绝缘基态。这一个人研究人员奖将支持一个研究项目，该项目将试图解决我们对SI转变的理解中的这些突出问题。解决这些问题的关键是将参数空间扩展到非常低的温度以确保在关键区域进行测量，仔细屏蔽电气引线中产生的外部噪声和热噪声，以及确定样品的结构。超电子密度的临界指数将通过测量穿透深度来确定，避免了有限尺寸标度在确定指数时的陷阱。还将通过施加磁场和控制耗散来调整跃迁。此外，还将通过改变有机超导二维电子气的载流子浓度来调谐SI相变。这项基础性工作对超导在纳米尺度上的深远技术应用具有潜在的重要意义。它是物理学博士生的重要培训基地，为他们提供了极其广泛的研究技能。由外部控制参数(如压力、磁场或载流子浓度)而不是由温度调节的相变称为量子相变。这些零温度转变是由海森堡测不准原理所支配的量子涨落驱动的，而不是像水变成蒸汽或冰那样由热涨落驱动的。出现量子相变的系统包括二维超导体、吸附在随机衬底上的4He、高迁移率的二维电子气、各种强关联磁系统和高T_c超导体。这一个人研究人员奖支持一个项目，该项目专注于研究颗粒和均匀金属薄膜形式的二维超导体中的超导体-绝缘体转变，以及有机晶体的真正二维场效应晶体管配置。将要解决的问题包括基本物理模型的性质，以及是否存在将超导和绝缘基态分开的明显的金属相。这项基础性工作对纳米技术和高温超导的深远技术应用具有潜在的重要意义。该项目在样品的制作和表征方面取得了新的技术突破，并通过发展非常广泛的研究技能为物理学博士候选人提供了重要的培训。

Superconductor-insulator (SI) transitions in ultrathin metal films and organic crystal field effect transistor configurations can be tuned by external control parameters and are believed to be zero-temperature quantum phase transitions, driven by quantum rather than thermal fluctuations. The nature of the underlying physical models of SI transitions is uncertain, as existing experiments do not distinguish between competing fermionic and bosonic descriptions, and there may be a distinct metallic phase separating the superconducting and insulating ground states. This individual investigator award will support a research project that will attempt to resolve these outstanding questions in our understanding of SI transitions. Keys to resolving the issues are the extension of the parameter space to very low temperatures to insure measurements in the critical regime, careful shielding from both external noise and thermal noise generated in electrical leads, and determining the structure of samples. The super-electron density critical exponent will be determined by measuring the penetration depth, avoiding the pitfalls of finite-size scaling in determining exponents. Transitions will also be tuned by applying magnetic fields, and by controlling dissipation. In addition, the SI transition will also be tuned by changing the carrier concentration of organic superconducting two-dimensional electron gases. This fundamental work is potentially significant for far-reaching technological applications of superconductivity at the nanoscale. It serves as an important training ground for doctoral students in physics, providing them with an extremely broad range of research skills. Phase transitions tuned by an external control parameter such as pressure, magnetic field, or carrier concentration, rather than temperature are called quantum phase transitions. These zero-temperature transitions are driven by quantum fluctuations governed by Heisenberg's uncertainty principle, rather than by thermal fluctuations, as when water changes to steam or ice. Systems that exhibit quantum phase transitions include two-dimensional superconductors, 4He adsorbed on random substrates, high-mobility two-dimensional electron gases, various strongly-correlated magnetic systems, and high-Tc superconductors. This individual investigator award supports a project that is focused on studying superconductor-insulator transitions in two-dimensional superconductors in the form of granular and homogenous metallic films, and in truly two-dimensional field-effect transistor configurations of organic crystals. The issues that will be addressed include the nature of the underlying physical models and whether there is a distinct metallic phase separating the superconducting and insulating ground states. This fundamental work is potentially significant for far-reaching technological applications in both nanotechnology and high-temperature superconductivity. The program breaks new ground technologically in the fabrication and characterization of samples, and provides important training for doctoral candidates in physics by developing an extremely broad range of research skills.