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.

技术摘要这个项目将继续探索简单的二维金属系统中的超导体-绝缘体(SI)转变的实验。这些相变被认为是连续的量子相变(QPT)。QPT是当代凝聚态物理中的一个重要范式。与热驱动相变不同的是，QPT在零温度下发生，基态随着外部参数的变化而改变。与QPTs相关的涨落是量子力学的，而不是经典的。在临界区的非零温度下的测量可以揭示这些量子涨落，并可以用来描述它们。其他显示QPTs的系统包括二维电子气、具有强关联电子的化合物和某些冷原子系统。将进行的实验将回答一些公开的问题，这些问题涉及管理SI转变的物理模型的性质，这些模型通过外部参数(如无序、耗散、电荷密度和磁场)进行调整，绝缘状态的性质，材料属性的影响，以及经常出现新物理的临界区的性质。研究将包括输运和磁输运、电噪声、能斯特效应和转变时的电子可压缩性的测量。这项工作需要先进的实验科学工具，包括纳米制造和超低温物理。该项目将支持博士生和本科生的教育，为从学术界到高科技行业的科学职业生涯提供极好的培训。非技术摘要量子力学是描述亚微观世界的理论。值得当代关注的是它在宏观世界中扮演的角色的性质。热力学相变是无序相和有序相之间的相变。它们的微观机制总是量子力学的。在这样的转变中，宏观行为，特别是在转变附近发现的有序度的空间和时间波动，是经典的。量子相变是在绝对零度下发生的无序和有序相之间的相变。它们不是由温度控制，而是由磁场、压力或电荷密度等外部参数的变化控制。与热力学转变不同的是，它们的波动是量子力学的，它们在非零温度下持续存在，从而允许他们进行研究。本项目致力于研究最简单的量子相变，即二维超导体-绝缘体相变。将进行的实验将回答与这些转变相关的宏观量子涨落的公开问题，并探索在转变附近出现的新物理。这项工作对其他领域的研究也有意义，因为量子相变发生在二维电子气、具有强关联电子的化合物和某些冷原子系统中。拟议的实验需要先进的实验科学工具，包括纳米制造和超低温物理。该项目将支持博士生和本科生的教育，为从学术界到高科技行业的科学职业生涯提供极好的培训。