Superconductor-Insulator Transitions in Disordered Ultrathin Films

技术摘要这个项目将进行探测超导体的实验。绝缘体（SI）在简单的二维金属系统的转变。这些转变被认为是连续量子相变（QPT）。QPT是当代凝聚态物理学的一个重要范式。 与热驱动相变相反，QPT发生在零温度下，基态响应于外部参数的变化而改变。与QPT相关的涨落是量子力学的，而不是经典的。 在临界区非零温度下的测量可以揭示这些量子涨落，并可以用来表征它们。 其他表现出QPT的系统包括二维电子气体、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有关物理模型的性质与外部参数，如无序，耗散，电荷密度和磁场，绝缘状态的性质，材料特性的影响，以及临界区域的性质，其中新的物理经常出现调整SI过渡的开放性问题。调查将包括运输和磁运输，电噪声，能斯特效应，和电子的可压缩性在过渡的测量。 这项工作需要先进的实验科学工具，包括纳米纤维和超低温物理学。该项目将支持博士生和本科生的教育方式，是优秀的培训，从学术界到高科技产业的科学事业。非技术摘要量子力学是描述亚微观世界的理论。 当代利息的本质是它在宏观世界中的作用。 热力学相变是无序相和有序相之间的转变。 它们的微观机制总是量子力学的。 在这样的过渡的宏观行为，特别是空间和时间的波动的程度附近的过渡，发现是经典的。 量子相变是无序相和有序相之间的转变，发生在绝对零度。 它们不是由温度控制，而是由外部参数的变化控制，如磁场、压力或电荷密度。 与热力学转变相反，它们的涨落是量子力学的，并且它们在非零温度下持续存在，从而允许它们的研究。 该项目的重点是研究最简单的量子相变，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开放性问题，并探索在转变附近出现的新物理。这项工作对其他研究领域也有影响，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，包括纳米纤维和超低温物理学。该项目将支持博士生和本科生的教育方式，是优秀的培训，从学术界到高科技产业的科学事业。

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.