Superconductor-Insulator Transitions in Disordered Ultrathin Films

无序超薄膜中的超导体-绝缘体转变

• 批准号: 0854752
• 负责人: Allen Goldman
• 金额: $ 60万
• 依托单位: University of Minnesota-Twin Cities
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-06-01 至 2013-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0854752&HistoricalAwards=false
• 关键词: Superconductor; Insulator; Transitions; Disordered; Ultrathin

Technical AbstractThis project will pursue experiments that probe superconductor?insulator (SI) transitions in simple two-dimensional metallic systems. These transitions are believed to be continuous quantum phase transitions (QPTs). The QPT is an important paradigm in contemporary condensed matter physics. A QPT, in contrast with a thermally driven phase transition, occurs at zero temperature with the ground state being changed in response to the variation of an external parameter. The fluctuations associated with QPTs are quantum mechanical rather than classical. Measurements at nonzero temperature in the critical regime can reveal these quantum fluctuations and can be used to characterize them. Other systems exhibiting QPTs include two-dimensional electron gases, compounds with strongly correlated electrons, and certain cold atom systems. The experiments that will be pursued will answer open questions regarding the nature of physical models governing SI transitions tuned with external parameters such as disorder, dissipation, charge density, and magnetic field, the nature of the insulating state, the influence of material properties, and the nature of the critical region, where new physics often emerges. The investigations will include measurements of transport and magneto-transport, electrical noise, the Nernst effect, and the electronic compressibility at the transition. The work requires advanced tools of experimental science including nanofabrication and ultra-low temperature physics. This project will support the education of PhD students and undergraduates in a manner that is excellent training for scientific careers from academia to high technology industries.Nontechnical AbstractQuantum mechanics is the theory describing the sub-microscopic world. Of contemporary interest is the nature of its role in the macroscopic world. Thermodynamic phase transitions are transitions between disordered and ordered phases. Their microscopic mechanisms are always quantum mechanical. In such transitions the macroscopic behavior, in particular the spatial and temporal fluctuations of the degree of order found near the transition, is classical. Quantum phase transitions are transitions between disordered and ordered phases, occurring at absolute zero. Instead of temperature, they are controlled by changes in external parameters such as magnetic field, pressure or charge density. In contrast with thermodynamic transitions, their fluctuations are quantum mechanical, and they persist at nonzero temperatures thus allowing their study. This project is focused on the investigation of the simplest quantum phase transitions, superconductor-insulator transitions in two-dimensions. The experiments that will be pursued will answer open questions regarding the macroscopic quantum fluctuations associated with these transitions and explore new physics that emerges near the transitions. The work has implications for other areas of research as quantum phase transitions occur in two-dimensional electron gases, compounds with strongly correlated electrons, and certain cold atom systems. The proposed experiments require advanced tools of experimental science including nanofabrication and ultra-low temperature physics. This project will support the education of PhD students and undergraduates in a manner that is excellent training for scientific careers from academia to high technology industries.

技术摘要该项目将进行实验，以探测简单的二维金属系统中的超导体？绝缘体（SI）过渡。这些转变被认为是连续的量子相变（QPTS）。 QPT是当代冷凝物理物理学中的重要范式。 与热驱动相变的相反，QPT发生在零温度下，基态因外部参数的变化而改变。与QPT相关的波动是量子机械的，而不是经典的。 在临界机制中，在非零温度下的测量可以揭示这些量子波动，并且可以用来表征它们。 展示QPT的其他系统包括二维电子气体，具有强相关电子的化合物以及某些冷原子系统。 将要进行的实验将回答有关使用外部参数（例如混乱，耗散，电荷密度和磁场）调整的有关SI转变的物理模型的性质的开放问题，绝缘状态的性质，材料特性的影响以及关键区域的性质以及新物理学经常出现的关键区域的性质。研究将包括测量运输和磁通电场，电噪声，Nernst效应以及过渡时的电子可压缩性。 这项工作需要实验科学的先进工具，包括纳米化和超低温度物理。该项目将以对从学术界到高科技行业的科学职业进行出色培训的方式来支持博士生和本科生的教育。本地技术抽象Quantum Mechanics是描述亚微镜世界的理论。 当代兴趣是其在宏观世界中作用的本质。 热力学相变是无序和有序相之间的转变。 它们的微观机制始终是量子机械的。 在这种过渡中，宏观行为，特别是在过渡附近发现的秩序程度的空间和时间波动是经典的。 量子相变是无序相和有序相之间的转变，发生在绝对零。 而不是温度，它们由外部参数（例如磁场，压力或电荷密度）的变化控制。 与热力学转变相反，它们的波动是量子机械的，并且在非零温度下持续存在，因此可以进行研究。 该项目的重点是研究最简单的量子相变，二维中的超导体 - 绝缘体转变。 将要进行的实验将回答有关与这些过渡相关的宏观量子波动的开放问题，并探索在过渡附近出现的新物理学。这项工作对其他研究领域具有影响，因为量子相变发生在二维电子气体，具有强相关电子的化合物以及某些冷原子系统中。 提出的实验需要实验科学的高级工具，包括纳米化和超低温度物理学。该项目将以一种为从学术界到高科技行业的科学职业提供出色培训的方式来支持博士生和本科生的教育。